Feature: Settings screen with account, theme, profile, reset + credits

Backend:
- New GET/PUT /api/me endpoint to read and update the authenticated
  user's profile (currently display_name). UserStore.UpdateDisplayName.
- Wired into the authed router.

App:
- New SettingsScreen + SettingsViewModel with five sections:
  * Account & Sync: login status, email, server URL, logout, connect.
  * Profile: edit display name (pushed to PUT /api/me when logged in).
  * Appearance: System / Light / Dark theme switch, persisted in
    SessionManager and applied via MitbringslTheme(sessionManager).
  * Data: 'Reset local data' wipes Room tables (server data kept).
  * About: version, 'Developed by Janik Dietz', and credits to
    GLM-5.2 + Gemini 3.6 Flash.
- Theme.kt now reads the user's theme preference (StateFlow) instead
  of only the system default; MainActivity passes SessionManager in.
- Navigation: new SettingsNavKey; settings gear icon in ListsScreen
  top bar; Settings links back to the Sync/Account screen.
- DTOs/API: UpdateMeRequestDto + getMe()/updateMe() for /api/me.

android/app/src/main/java/com/example/mitbringsl/MainActivity.kt

@@ -28,7 +28,7 @@ class MainActivity : ComponentActivity() {
 
         enableEdgeToEdge()
         setContent {
-            MitbringslTheme {
+            MitbringslTheme(sessionManager = sessionManager) {
                 Surface(
                     modifier = Modifier.fillMaxSize(),
                     color = MaterialTheme.colorScheme.background

android/app/src/main/java/com/example/mitbringsl/Navigation.kt

@@ -8,6 +8,7 @@ import com.example.mitbringsl.data.auth.SessionManager
 import com.example.mitbringsl.ui.auth.AuthScreen
 import com.example.mitbringsl.ui.detail.ListDetailScreen
 import com.example.mitbringsl.ui.lists.ListsScreen
+import com.example.mitbringsl.ui.settings.SettingsScreen
 
 @Composable
 fun MainNavigation(sessionManager: SessionManager) {
@@ -25,6 +26,9 @@ fun MainNavigation(sessionManager: SessionManager) {
                     },
                     onOpenSync = {
                         backStack.add(AuthNavKey)
+                    },
+                    onOpenSettings = {
+                        backStack.add(SettingsNavKey)
                     }
                 )
             }
@@ -35,6 +39,14 @@ fun MainNavigation(sessionManager: SessionManager) {
                     }
                 )
             }
+            entry<SettingsNavKey> {
+                SettingsScreen(
+                    onBack = { backStack.removeLastOrNull() },
+                    onOpenSync = {
+                        backStack.add(AuthNavKey)
+                    }
+                )
+            }
             entry<ListDetailNavKey> { key ->
                 ListDetailScreen(
                     listId = key.listId,

android/app/src/main/java/com/example/mitbringsl/NavigationKeys.kt

@@ -5,4 +5,5 @@ import kotlinx.serialization.Serializable
 
 @Serializable data object AuthNavKey : NavKey
 @Serializable data object ListsNavKey : NavKey
+@Serializable data object SettingsNavKey : NavKey
 @Serializable data class ListDetailNavKey(val listId: String) : NavKey

android/app/src/main/java/com/example/mitbringsl/data/auth/SessionManager.kt

@@ -29,6 +29,17 @@ class SessionManager @Inject constructor(
     private val _serverUrl = MutableStateFlow(getServerUrl())
     val serverUrl: StateFlow<String> = _serverUrl.asStateFlow()
 
+    // Theme preference: "system" | "light" | "dark"
+    private val _themeMode = MutableStateFlow(getThemeMode())
+    val themeMode: StateFlow<String> = _themeMode.asStateFlow()
+
+    fun getThemeMode(): String = prefs.getString("theme_mode", null) ?: "system"
+
+    fun saveThemeMode(mode: String) {
+        prefs.edit { putString("theme_mode", mode) }
+        _themeMode.value = mode
+    }
+
     fun getServerUrl(): String {
         return prefs.getString("server_url", null) ?: BuildConfig.BASE_URL
     }

android/app/src/main/java/com/example/mitbringsl/data/remote/api/MitbringslApi.kt

@@ -27,6 +27,14 @@ interface MitbringslApi {
     @POST("auth/logout")
     suspend fun logout(): Response<Unit>
 
+    // --- Profile (/api/me) --------------------------------------------------
+
+    @GET("api/me")
+    suspend fun getMe(): Response<UserDto>
+
+    @PUT("api/me")
+    suspend fun updateMe(@Body body: UpdateMeRequestDto): Response<UserDto>
+
     // --- Lists --------------------------------------------------------------
 
     @GET("api/lists")

android/app/src/main/java/com/example/mitbringsl/data/remote/dto/Dtos.kt

@@ -41,6 +41,11 @@ data class UserDto(
     @SerialName("display_name") val displayName: String = "",
 )
 
+@Serializable
+data class UpdateMeRequestDto(
+    @SerialName("display_name") val displayName: String? = null,
+)
+
 // ---------------------------------------------------------------------------
 // Lists
 // ---------------------------------------------------------------------------

android/app/src/main/java/com/example/mitbringsl/theme/Theme.kt

@@ -8,7 +8,10 @@ import androidx.compose.material3.dynamicDarkColorScheme
 import androidx.compose.material3.dynamicLightColorScheme
 import androidx.compose.material3.lightColorScheme
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
 import androidx.compose.ui.platform.LocalContext
+import com.example.mitbringsl.data.auth.SessionManager
 
 private val DarkColorScheme = darkColorScheme(primary = Purple80, secondary = PurpleGrey80, tertiary = Pink80)
 
@@ -17,25 +20,27 @@ private val LightColorScheme =
     primary = Purple40,
     secondary = PurpleGrey40,
     tertiary = Pink40,
-
-    /* Other default colors to override
-    background = Color(0xFFFFFBFE),
-    surface = Color(0xFFFFFBFE),
-    onPrimary = Color.White,
-    onSecondary = Color.White,
-    onTertiary = Color.White,
-    onBackground = Color(0xFF1C1B1F),
-    onSurface = Color(0xFF1C1B1F),
-    */
   )
 
+/**
+ * App theme. The dark/light mode is driven by the user's preference stored in
+ * [SessionManager] ("system" | "light" | "dark"), defaulting to the system setting.
+ */
 @Composable
 fun MitbringslTheme(
-  darkTheme: Boolean = isSystemInDarkTheme(),
+  sessionManager: SessionManager,
   // Dynamic color is available on Android 12+
   dynamicColor: Boolean = true,
   content: @Composable () -> Unit,
 ) {
+  val mode by sessionManager.themeMode.collectAsState()
+  val systemDark = isSystemInDarkTheme()
+  val darkTheme = when (mode) {
+    "light" -> false
+    "dark" -> true
+    else -> systemDark // "system" or any unknown value
+  }
+
   val colorScheme =
     when {
       dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {

android/app/src/main/java/com/example/mitbringsl/ui/lists/ListsScreen.kt

@@ -14,6 +14,7 @@ import androidx.compose.material.icons.filled.CloudDone
 import androidx.compose.material.icons.filled.CloudOff
 import androidx.compose.material.icons.filled.Delete
 import androidx.compose.material.icons.filled.GroupAdd
+import androidx.compose.material.icons.filled.Settings
 import androidx.compose.material.icons.filled.ShoppingCart
 import androidx.compose.material.icons.filled.WifiOff
 import androidx.compose.material3.*
@@ -33,6 +34,7 @@ import com.example.mitbringsl.data.local.entity.ListEntity
 fun ListsScreen(
     onSelectList: (String) -> Unit,
     onOpenSync: () -> Unit,
+    onOpenSettings: () -> Unit,
     modifier: Modifier = Modifier,
     viewModel: ListsViewModel = hiltViewModel(),
 ) {
@@ -56,6 +58,12 @@ fun ListsScreen(
                     )
                 },
                 actions = {
+                    IconButton(onClick = onOpenSettings) {
+                        Icon(
+                            imageVector = Icons.Default.Settings,
+                            contentDescription = "Einstellungen"
+                        )
+                    }
                     IconButton(onClick = {
                         if (isLoggedIn) {
                             showJoinDialog = true

android/app/src/main/java/com/example/mitbringsl/ui/settings/SettingsScreen.kt

@@ -0,0 +1,410 @@
+package com.example.mitbringsl.ui.settings
+
+import androidx.compose.foundation.layout.*
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.verticalScroll
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material.icons.filled.AutoAwesome
+import androidx.compose.material.icons.filled.Brightness6
+import androidx.compose.material.icons.filled.CloudOff
+import androidx.compose.material.icons.filled.DeleteForever
+import androidx.compose.material.icons.filled.Dns
+import androidx.compose.material.icons.filled.Person
+import androidx.compose.material3.*
+import androidx.compose.runtime.*
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import androidx.hilt.navigation.compose.hiltViewModel
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun SettingsScreen(
+    onBack: () -> Unit,
+    onOpenSync: () -> Unit,
+    modifier: Modifier = Modifier,
+    viewModel: SettingsViewModel = hiltViewModel(),
+) {
+    val uiState by viewModel.uiState.collectAsStateWithLifecycle()
+    val isLoggedIn by viewModel.sessionManager.isLoggedIn.collectAsStateWithLifecycle()
+    val currentServerUrl by viewModel.sessionManager.serverUrl.collectAsStateWithLifecycle()
+    val userEmail = viewModel.sessionManager.getUserEmail()
+    val themeMode by viewModel.sessionManager.themeMode.collectAsStateWithLifecycle()
+
+    var showResetDialog by remember { mutableStateOf(false) }
+    var showLogoutDialog by remember { mutableStateOf(false) }
+
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = { Text("Einstellungen", fontWeight = FontWeight.Bold) },
+                navigationIcon = {
+                    IconButton(onClick = onBack) {
+                        Icon(
+                            imageVector = Icons.AutoMirrored.Filled.ArrowBack,
+                            contentDescription = "Zurück"
+                        )
+                    }
+                },
+                colors = TopAppBarDefaults.topAppBarColors(
+                    containerColor = MaterialTheme.colorScheme.surface
+                )
+            )
+        },
+        modifier = modifier
+    ) { padding ->
+        Column(
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(padding)
+                .verticalScroll(rememberScrollState())
+                .padding(16.dp),
+            verticalArrangement = Arrangement.spacedBy(16.dp)
+        ) {
+            // --- Account / Sync -------------------------------------------------
+            SectionHeader(text = "Account & Sync")
+            Card(shape = RoundedCornerShape(16.dp)) {
+                Column(modifier = Modifier.padding(16.dp)) {
+                    if (isLoggedIn) {
+                        ProfileRow(label = "Angemeldet als", value = userEmail ?: "—")
+                        ProfileRow(
+                            label = "Anzeigename",
+                            value = uiState.serverDisplayName.ifBlank { "—" }
+                        )
+                        Spacer(modifier = Modifier.height(12.dp))
+                        OutlinedButton(
+                            onClick = onOpenSync,
+                            modifier = Modifier.fillMaxWidth(),
+                            shape = RoundedCornerShape(12.dp)
+                        ) {
+                            Icon(imageVector = Icons.Default.Dns, contentDescription = null)
+                            Spacer(modifier = Modifier.width(8.dp))
+                            Text("Server-Verbindung verwalten")
+                        }
+                        Spacer(modifier = Modifier.height(8.dp))
+                        OutlinedButton(
+                            onClick = { showLogoutDialog = true },
+                            modifier = Modifier.fillMaxWidth(),
+                            shape = RoundedCornerShape(12.dp),
+                            colors = ButtonDefaults.outlinedButtonColors(
+                                contentColor = MaterialTheme.colorScheme.error
+                            )
+                        ) {
+                            Icon(imageVector = Icons.Default.CloudOff, contentDescription = null)
+                            Spacer(modifier = Modifier.width(8.dp))
+                            Text("Abmelden")
+                        }
+                    } else {
+                        Text(
+                            text = "Nicht verbunden",
+                            style = MaterialTheme.typography.bodyMedium,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant
+                        )
+                        Spacer(modifier = Modifier.height(4.dp))
+                        Text(
+                            text = "Server: $currentServerUrl",
+                            style = MaterialTheme.typography.bodySmall,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant
+                        )
+                        Spacer(modifier = Modifier.height(12.dp))
+                        Button(
+                            onClick = onOpenSync,
+                            modifier = Modifier.fillMaxWidth(),
+                            shape = RoundedCornerShape(12.dp)
+                        ) {
+                            Text("Mit Server verbinden")
+                        }
+                    }
+                }
+            }
+
+            // --- Profil (Display Name) -----------------------------------------
+            if (isLoggedIn) {
+                SectionHeader(text = "Profil")
+                Card(shape = RoundedCornerShape(16.dp)) {
+                    Column(modifier = Modifier.padding(16.dp)) {
+                        OutlinedTextField(
+                            value = uiState.displayNameInput,
+                            onValueChange = viewModel::onDisplayNameChanged,
+                            label = { Text("Anzeigename") },
+                            singleLine = true,
+                            shape = RoundedCornerShape(12.dp),
+                            modifier = Modifier.fillMaxWidth(),
+                            enabled = !uiState.isSaving
+                        )
+                        Spacer(modifier = Modifier.height(12.dp))
+                        Button(
+                            onClick = viewModel::saveDisplayName,
+                            enabled = !uiState.isSaving && uiState.displayNameInput != uiState.serverDisplayName,
+                            modifier = Modifier.fillMaxWidth(),
+                            shape = RoundedCornerShape(12.dp)
+                        ) {
+                            if (uiState.isSaving) {
+                                CircularProgressIndicator(
+                                    modifier = Modifier.size(18.dp),
+                                    strokeWidth = 2.dp
+                                )
+                            } else {
+                                Icon(imageVector = Icons.Default.Person, contentDescription = null)
+                                Spacer(modifier = Modifier.width(8.dp))
+                                Text("Speichern")
+                            }
+                        }
+                    }
+                }
+            }
+
+            // --- Theme ---------------------------------------------------------
+            SectionHeader(text = "Erscheinungsbild")
+            Card(shape = RoundedCornerShape(16.dp)) {
+                Column(modifier = Modifier.padding(16.dp)) {
+                    Row(verticalAlignment = Alignment.CenterVertically) {
+                        Icon(imageVector = Icons.Default.Brightness6, contentDescription = null)
+                        Spacer(modifier = Modifier.width(12.dp))
+                        Text("Design", style = MaterialTheme.typography.bodyLarge)
+                    }
+                    Spacer(modifier = Modifier.height(12.dp))
+                    ThemeOptionRow(
+                        label = "System",
+                        selected = themeMode == "system",
+                        onClick = { viewModel.setThemeMode("system") }
+                    )
+                    ThemeOptionRow(
+                        label = "Hell",
+                        selected = themeMode == "light",
+                        onClick = { viewModel.setThemeMode("light") }
+                    )
+                    ThemeOptionRow(
+                        label = "Dunkel",
+                        selected = themeMode == "dark",
+                        onClick = { viewModel.setThemeMode("dark") }
+                    )
+                }
+            }
+
+            // --- Daten zurücksetzen --------------------------------------------
+            SectionHeader(text = "Daten")
+            Card(shape = RoundedCornerShape(16.dp)) {
+                Column(modifier = Modifier.padding(16.dp)) {
+                    Text(
+                        text = "Lokale Daten löschen",
+                        style = MaterialTheme.typography.bodyLarge,
+                        fontWeight = FontWeight.Medium
+                    )
+                    Spacer(modifier = Modifier.height(4.dp))
+                    Text(
+                        text = "Entfernt alle Listen und Items von diesem Gerät. Server-Daten bleiben erhalten und können neu synchronisiert werden.",
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant
+                    )
+                    Spacer(modifier = Modifier.height(12.dp))
+                    OutlinedButton(
+                        onClick = { showResetDialog = true },
+                        modifier = Modifier.fillMaxWidth(),
+                        shape = RoundedCornerShape(12.dp),
+                        colors = ButtonDefaults.outlinedButtonColors(
+                            contentColor = MaterialTheme.colorScheme.error
+                        )
+                    ) {
+                        Icon(imageVector = Icons.Default.DeleteForever, contentDescription = null)
+                        Spacer(modifier = Modifier.width(8.dp))
+                        Text("Lokale Daten zurücksetzen")
+                    }
+                }
+            }
+
+            // --- Über / Credits ------------------------------------------------
+            SectionHeader(text = "Über Mitbringsl")
+            Card(shape = RoundedCornerShape(16.dp)) {
+                Column(
+                    modifier = Modifier.padding(16.dp),
+                    horizontalAlignment = Alignment.CenterHorizontally
+                ) {
+                    Text(
+                        text = "Mitbringsl",
+                        style = MaterialTheme.typography.titleLarge,
+                        fontWeight = FontWeight.Bold
+                    )
+                    Text(
+                        text = "Version 1.0",
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant
+                    )
+                    Spacer(modifier = Modifier.height(16.dp))
+                    Text(
+                        text = "Entwickelt von",
+                        style = MaterialTheme.typography.labelMedium,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant
+                    )
+                    Text(
+                        text = "Janik Dietz",
+                        style = MaterialTheme.typography.titleMedium,
+                        fontWeight = FontWeight.SemiBold
+                    )
+                    Spacer(modifier = Modifier.height(16.dp))
+                    Row(verticalAlignment = Alignment.CenterVertically) {
+                        Icon(
+                            imageVector = Icons.Default.AutoAwesome,
+                            contentDescription = null,
+                            tint = MaterialTheme.colorScheme.primary,
+                            modifier = Modifier.size(16.dp)
+                        )
+                        Spacer(modifier = Modifier.width(6.dp))
+                        Text(
+                            text = "Mit Unterstützung durch",
+                            style = MaterialTheme.typography.labelMedium,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant
+                        )
+                    }
+                    Spacer(modifier = Modifier.height(8.dp))
+                    CreditItem(text = "GLM-5.2")
+                    CreditItem(text = "Gemini 3.6 Flash")
+                    Spacer(modifier = Modifier.height(12.dp))
+                    Text(
+                        text = "Local-First Einkaufslisten-App – werbefrei, selbstgehostet.",
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                        textAlign = TextAlign.Center
+                    )
+                }
+            }
+
+            // --- message / error toast-like ------------------------------------
+            if (uiState.message != null) {
+                Snackbar { Text(uiState.message!!) }
+            }
+            if (uiState.error != null) {
+                Snackbar(
+                    containerColor = MaterialTheme.colorScheme.errorContainer,
+                    contentColor = MaterialTheme.colorScheme.onErrorContainer
+                ) { Text(uiState.error!!) }
+            }
+
+            Spacer(modifier = Modifier.height(24.dp))
+        }
+    }
+
+    // --- dialogs -------------------------------------------------------------
+    if (showResetDialog) {
+        AlertDialog(
+            onDismissRequest = { showResetDialog = false },
+            title = { Text("Lokale Daten löschen?") },
+            text = {
+                Text(
+                    "Alle Listen und Items werden von diesem Gerät entfernt. " +
+                        "Diese Aktion kann nicht rückgängig gemacht werden. " +
+                        "Auf dem Server gespeicherte Daten bleiben erhalten."
+                )
+            },
+            confirmButton = {
+                Button(
+                    onClick = {
+                        viewModel.resetLocalData()
+                        showResetDialog = false
+                    },
+                    colors = ButtonDefaults.buttonColors(
+                        containerColor = MaterialTheme.colorScheme.error
+                    ),
+                    shape = RoundedCornerShape(12.dp)
+                ) {
+                    Text("Löschen")
+                }
+            },
+            dismissButton = {
+                TextButton(onClick = { showResetDialog = false }) { Text("Abbrechen") }
+            },
+            shape = RoundedCornerShape(24.dp)
+        )
+    }
+
+    if (showLogoutDialog) {
+        AlertDialog(
+            onDismissRequest = { showLogoutDialog = false },
+            title = { Text("Abmelden?") },
+            text = {
+                Text(
+                    "Du wirst von diesem Gerät abgemeldet. " +
+                        "Lokale Änderungen, die noch nicht synchronisiert wurden, gehen verloren."
+                )
+            },
+            confirmButton = {
+                Button(
+                    onClick = {
+                        viewModel.logout()
+                        showLogoutDialog = false
+                    },
+                    shape = RoundedCornerShape(12.dp)
+                ) {
+                    Text("Abmelden")
+                }
+            },
+            dismissButton = {
+                TextButton(onClick = { showLogoutDialog = false }) { Text("Abbrechen") }
+            },
+            shape = RoundedCornerShape(24.dp)
+        )
+    }
+}
+
+@Composable
+private fun SectionHeader(text: String) {
+    Text(
+        text = text,
+        style = MaterialTheme.typography.titleSmall,
+        fontWeight = FontWeight.Bold,
+        color = MaterialTheme.colorScheme.primary,
+        modifier = Modifier.padding(top = 8.dp, bottom = 4.dp)
+    )
+}
+
+@Composable
+private fun ProfileRow(label: String, value: String) {
+    Column(modifier = Modifier.padding(vertical = 4.dp)) {
+        Text(
+            text = label,
+            style = MaterialTheme.typography.labelMedium,
+            color = MaterialTheme.colorScheme.onSurfaceVariant
+        )
+        Text(
+            text = value,
+            style = MaterialTheme.typography.bodyLarge,
+            fontWeight = FontWeight.Medium
+        )
+    }
+}
+
+@Composable
+private fun ThemeOptionRow(label: String, selected: Boolean, onClick: () -> Unit) {
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .padding(vertical = 4.dp),
+        verticalAlignment = Alignment.CenterVertically
+    ) {
+        RadioButton(selected = selected, onClick = onClick)
+        Spacer(modifier = Modifier.width(8.dp))
+        Text(label, style = MaterialTheme.typography.bodyLarge)
+    }
+}
+
+@Composable
+private fun CreditItem(text: String) {
+    Surface(
+        color = MaterialTheme.colorScheme.secondaryContainer.copy(alpha = 0.6f),
+        shape = RoundedCornerShape(20.dp)
+    ) {
+        Text(
+            text = text,
+            style = MaterialTheme.typography.bodyMedium,
+            fontWeight = FontWeight.Medium,
+            color = MaterialTheme.colorScheme.onSecondaryContainer,
+            modifier = Modifier.padding(horizontal = 16.dp, vertical = 6.dp)
+        )
+    }
+}

android/app/src/main/java/com/example/mitbringsl/ui/settings/SettingsViewModel.kt

@@ -0,0 +1,144 @@
+package com.example.mitbringsl.ui.settings
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import com.example.mitbringsl.data.auth.AuthRepository
+import com.example.mitbringsl.data.auth.SessionManager
+import com.example.mitbringsl.data.local.AppDatabase
+import com.example.mitbringsl.data.remote.api.MitbringslApi
+import com.example.mitbringsl.data.remote.dto.UpdateMeRequestDto
+import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.launch
+import javax.inject.Inject
+
+data class SettingsUiState(
+    val isLoading: Boolean = false,
+    val isSaving: Boolean = false,
+    val displayNameInput: String = "",
+    val serverDisplayName: String = "",
+    val message: String? = null,
+    val error: String? = null,
+)
+
+@HiltViewModel
+class SettingsViewModel @Inject constructor(
+    private val api: MitbringslApi,
+    private val authRepository: AuthRepository,
+    private val db: AppDatabase,
+    val sessionManager: SessionManager,
+) : ViewModel() {
+
+    private val _uiState = MutableStateFlow(SettingsUiState())
+    val uiState: StateFlow<SettingsUiState> = _uiState.asStateFlow()
+
+    init {
+        loadProfile()
+    }
+
+    /** Loads the display name from the server (if logged in) or falls back to local. */
+    fun loadProfile() {
+        if (!sessionManager.isLoggedIn.value) {
+            _uiState.update { it.copy(displayNameInput = "", serverDisplayName = "") }
+            return
+        }
+        viewModelScope.launch {
+            _uiState.update { it.copy(isLoading = true, error = null) }
+            try {
+                val resp = api.getMe()
+                if (resp.isSuccessful && resp.body() != null) {
+                    val name = resp.body()!!.displayName
+                    _uiState.update {
+                        it.copy(
+                            isLoading = false,
+                            displayNameInput = name,
+                            serverDisplayName = name,
+                        )
+                    }
+                } else {
+                    _uiState.update {
+                        it.copy(isLoading = false, error = "Profil konnte nicht geladen werden.")
+                    }
+                }
+            } catch (e: Exception) {
+                _uiState.update {
+                    it.copy(isLoading = false, error = e.localizedMessage ?: "Netzwerkfehler")
+                }
+            }
+        }
+    }
+
+    fun onDisplayNameChanged(value: String) {
+        _uiState.update { it.copy(displayNameInput = value, message = null, error = null) }
+    }
+
+    /** Pushes the display name to the server (only when logged in). */
+    fun saveDisplayName() {
+        if (!sessionManager.isLoggedIn.value) {
+            _uiState.update { it.copy(message = "Nicht verbunden – Änderung nur lokal möglich.") }
+            return
+        }
+        val name = _uiState.value.displayNameInput.trim()
+        viewModelScope.launch {
+            _uiState.update { it.copy(isSaving = true, error = null, message = null) }
+            try {
+                val resp = api.updateMe(UpdateMeRequestDto(displayName = name))
+                if (resp.isSuccessful && resp.body() != null) {
+                    _uiState.update {
+                        it.copy(
+                            isSaving = false,
+                            serverDisplayName = resp.body()!!.displayName,
+                            message = "Anzeigename gespeichert.",
+                        )
+                    }
+                } else {
+                    _uiState.update {
+                        it.copy(isSaving = false, error = "Speichern fehlgeschlagen (HTTP ${resp.code()}).")
+                    }
+                }
+            } catch (e: Exception) {
+                _uiState.update {
+                    it.copy(isSaving = false, error = e.localizedMessage ?: "Netzwerkfehler")
+                }
+            }
+        }
+    }
+
+    fun setThemeMode(mode: String) {
+        sessionManager.saveThemeMode(mode)
+    }
+
+    /** Logs the user out. */
+    fun logout() {
+        viewModelScope.launch {
+            authRepository.logout()
+        }
+    }
+
+    /**
+     * Wipes all local data (lists, items, op_log) – the destructive reset.
+     * Server data is NOT affected; the user can re-sync after logging in again.
+     */
+    fun resetLocalData() {
+        viewModelScope.launch {
+            _uiState.update { it.copy(isLoading = true, error = null) }
+            try {
+                db.clearAllTables()
+                _uiState.update {
+                    it.copy(isLoading = false, message = "Lokale Daten wurden gelöscht.")
+                }
+            } catch (e: Exception) {
+                _uiState.update {
+                    it.copy(isLoading = false, error = e.localizedMessage ?: "Löschen fehlgeschlagen.")
+                }
+            }
+        }
+    }
+
+    fun clearMessage() {
+        _uiState.update { it.copy(message = null, error = null) }
+    }
+}

backend/internal/auth/user.go

@@ -114,6 +114,27 @@ func (s *UserStore) GetByOIDCSubject(ctx context.Context, issuer, subject string
 	return u, nil
 }
 
+// UpdateDisplayName sets the display_name of the user with the given id.
+// An empty displayName clears the field (stores NULL).
+func (s *UserStore) UpdateDisplayName(ctx context.Context, id uuid.UUID, displayName string) (User, error) {
+	const q = `
+		UPDATE users SET display_name = NULLIF($2, ''), updated_at = now()
+		WHERE id = $1
+		RETURNING id, email, password_hash, oidc_subject, oidc_issuer, display_name`
+	var u User
+	var dn *string
+	err := s.pool.QueryRow(ctx, q, id, displayName).
+		Scan(&u.ID, &u.Email, &u.PasswordHash, &u.OIDCSubject, &u.OIDCIssuer, &dn)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return User{}, ErrUserNotFound
+		}
+		return User{}, fmt.Errorf("update display name: %w", err)
+	}
+	u.DisplayName = dn
+	return u, nil
+}
+
 // CreateOIDCUser inserts a new user for an OIDC login. The user has no password
 // (password_hash is NULL) and is identified by (issuer, subject). email may be
 // empty if the IdP did not provide one; we store a synthesized placeholder so

backend/internal/httpapi/api.go

@@ -21,6 +21,7 @@ type API struct {
 	ops     *OpsHandler
 	suggest *SuggestHandler
 	config  *ConfigHandler
+	me      *MeHandler
 }
 
 // NewAPI constructs the API with all handler groups.
@@ -51,6 +52,7 @@ func NewAPI(cfg *config.Config, pool *pgxpool.Pool) *API {
 		ops:     NewOpsHandler(opStore, listStore),
 		suggest: NewSuggestHandler(suggestStore),
 		config:  NewConfigHandler(cfg),
+		me:      NewMeHandler(users),
 	}
 }
 
@@ -85,6 +87,8 @@ func (a *API) Handler() http.Handler {
 	mux.HandleFunc("POST /auth/logout", a.auth.Logout)
 
 	// --- authenticated API endpoints ---
+	mux.Handle("GET /api/me",             a.RequireAuth(http.HandlerFunc(a.me.Get)))
+	mux.Handle("PUT /api/me",             a.RequireAuth(http.HandlerFunc(a.me.Update)))
 	mux.Handle("GET /api/lists",           a.RequireAuth(http.HandlerFunc(a.lists.List)))
 	mux.Handle("POST /api/lists",          a.RequireAuth(http.HandlerFunc(a.lists.Create)))
 	mux.Handle("POST /api/lists/join",     a.RequireAuth(http.HandlerFunc(a.lists.Join)))

backend/internal/httpapi/me.go

@@ -0,0 +1,76 @@
+package httpapi
+
+import (
+	"log/slog"
+	"net/http"
+	"strings"
+
+	"github.com/mitbringsl/backend/internal/auth"
+)
+
+// MeHandler exposes the authenticated user's own profile (/api/me).
+type MeHandler struct {
+	users *auth.UserStore
+}
+
+// NewMeHandler constructs a MeHandler.
+func NewMeHandler(users *auth.UserStore) *MeHandler {
+	return &MeHandler{users: users}
+}
+
+type updateMeRequest struct {
+	DisplayName *string `json:"display_name"` // nil = unchanged, "" = clear
+}
+
+// Get returns the current user's profile.
+// GET /api/me
+func (h *MeHandler) Get(w http.ResponseWriter, r *http.Request) {
+	userID, ok := userIDFromCtx(r)
+	if !ok {
+		renderError(w, http.StatusUnauthorized, "Unauthorized", "Missing user context.")
+		return
+	}
+	u, err := h.users.GetUserByID(r.Context(), userID)
+	if err != nil {
+		slog.Error("get me failed", "error", err, "user_id", userID)
+		renderError(w, http.StatusInternalServerError, "Internal error", "Could not load user.")
+		return
+	}
+	renderJSON(w, http.StatusOK, toUserDTO(u))
+}
+
+// Update changes editable fields of the current user (currently display_name).
+// PUT /api/me
+func (h *MeHandler) Update(w http.ResponseWriter, r *http.Request) {
+	userID, ok := userIDFromCtx(r)
+	if !ok {
+		renderError(w, http.StatusUnauthorized, "Unauthorized", "Missing user context.")
+		return
+	}
+	var req updateMeRequest
+	if !decodeJSON(w, r, &req) {
+		return
+	}
+
+	// Only update when display_name is provided in the body (pointer non-nil).
+	// Trimming to keep stored names tidy; an empty string clears the field.
+	if req.DisplayName == nil {
+		// Nothing to change – return the current profile.
+		u, err := h.users.GetUserByID(r.Context(), userID)
+		if err != nil {
+			renderError(w, http.StatusInternalServerError, "Internal error", "Could not load user.")
+			return
+		}
+		renderJSON(w, http.StatusOK, toUserDTO(u))
+		return
+	}
+
+	name := strings.TrimSpace(*req.DisplayName)
+	u, err := h.users.UpdateDisplayName(r.Context(), userID, name)
+	if err != nil {
+		slog.Error("update me failed", "error", err, "user_id", userID)
+		renderError(w, http.StatusInternalServerError, "Internal error", "Could not update user.")
+		return
+	}
+	renderJSON(w, http.StatusOK, toUserDTO(u))
+}