Refactor: Require active server connection for sharing and joining lists

- ListDetailScreen: hide Share action icon when not connected to a server (isLoggedIn == false)
- ListsScreen: show informative prompt dialog if user attempts to join a list without active server connection
- ListDetailViewModel: expose sessionManager to check auth state cleanly
- ADB reinstall & launch verified ✅

android/app/src/main/java/com/example/mitbringsl/ui/detail/ListDetailScreen.kt

@@ -45,6 +45,7 @@ fun ListDetailScreen(
     val query by viewModel.query.collectAsStateWithLifecycle()
     val suggestions by viewModel.suggestions.collectAsStateWithLifecycle()
     val inviteCode by viewModel.inviteCode.collectAsStateWithLifecycle()
+    val isLoggedIn by viewModel.sessionManager.isLoggedIn.collectAsStateWithLifecycle()
 
     val context = LocalContext.current
     var showShareDialog by remember { mutableStateOf(false) }
@@ -68,7 +69,8 @@ fun ListDetailScreen(
                     }
                 },
                 actions = {
-                    if (!inviteCode.isNullOrBlank()) {
+                    // Only allow sharing if the user is connected to a sync server
+                    if (isLoggedIn && !inviteCode.isNullOrBlank()) {
                         IconButton(onClick = { showShareDialog = true }) {
                             Icon(
                                 imageVector = Icons.Default.Share,

android/app/src/main/java/com/example/mitbringsl/ui/detail/ListDetailViewModel.kt

@@ -2,6 +2,7 @@ package com.example.mitbringsl.ui.detail
 
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
+import com.example.mitbringsl.data.auth.SessionManager
 import com.example.mitbringsl.data.local.entity.ItemEntity
 import com.example.mitbringsl.data.remote.api.MitbringslApi
 import com.example.mitbringsl.data.repository.ShoppingRepository
@@ -17,6 +18,7 @@ import javax.inject.Inject
 class ListDetailViewModel @Inject constructor(
     private val repository: ShoppingRepository,
     private val api: MitbringslApi,
+    val sessionManager: SessionManager,
 ) : ViewModel() {
 
     private val _listId = MutableStateFlow<String?>(null)

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

@@ -44,6 +44,7 @@ fun ListsScreen(
 
     var showAddDialog by remember { mutableStateOf(false) }
     var showJoinDialog by remember { mutableStateOf(false) }
+    var showNeedSyncDialog by remember { mutableStateOf(false) }
 
     Scaffold(
         topBar = {
@@ -55,7 +56,13 @@ fun ListsScreen(
                     )
                 },
                 actions = {
-                    IconButton(onClick = { showJoinDialog = true }) {
+                    IconButton(onClick = {
+                        if (isLoggedIn) {
+                            showJoinDialog = true
+                        } else {
+                            showNeedSyncDialog = true
+                        }
+                    }) {
                         Icon(
                             imageVector = Icons.Default.GroupAdd,
                             contentDescription = "Liste beitreten"
@@ -170,7 +177,13 @@ fun ListsScreen(
                         )
                         Spacer(modifier = Modifier.height(16.dp))
                         OutlinedButton(
-                            onClick = { showJoinDialog = true },
+                            onClick = {
+                                if (isLoggedIn) {
+                                    showJoinDialog = true
+                                } else {
+                                    showNeedSyncDialog = true
+                                }
+                            },
                             shape = RoundedCornerShape(12.dp)
                         ) {
                             Icon(imageVector = Icons.Default.GroupAdd, contentDescription = null)
@@ -221,6 +234,36 @@ fun ListsScreen(
             }
         )
     }
+
+    if (showNeedSyncDialog) {
+        AlertDialog(
+            onDismissRequest = { showNeedSyncDialog = false },
+            title = { Text("Server-Verbindung erforderlich") },
+            text = {
+                Text(
+                    text = "Um einer geteilten Einkaufsliste beizutreten oder eigene Listen zu teilen, verbinde dich bitte zuerst mit deinem Mitbringsl Sync-Server.",
+                    style = MaterialTheme.typography.bodyMedium
+                )
+            },
+            confirmButton = {
+                Button(
+                    onClick = {
+                        showNeedSyncDialog = false
+                        onOpenSync()
+                    },
+                    shape = RoundedCornerShape(12.dp)
+                ) {
+                    Text("Jetzt verbinden")
+                }
+            },
+            dismissButton = {
+                TextButton(onClick = { showNeedSyncDialog = false }) {
+                    Text("Abbrechen")
+                }
+            },
+            shape = RoundedCornerShape(24.dp)
+        )
+    }
 }
 
 @Composable