feat(android): add "change cover" action on the detail screen

Mirrors the desktop DetailDialog's "Cover ändern…" button: opens the
online search pre-filled with the item's title and auto-searches, but
choosing a hit only replaces the item's cover URL instead of staging a
full edit draft.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

android/app/src/main/java/com/umt/tracker/data/LibraryRepository.kt

@@ -78,6 +78,9 @@ class LibraryRepository(
 
     suspend fun setRating(id: Long, rating: Int) = updateItem(id) { it.copy(rating = rating.coerceIn(0, 10)) }
 
+    /** Replaces the item's cover with a remote image URL (from a metadata provider). */
+    suspend fun setCover(id: Long, coverUrl: String) = updateItem(id) { it.copy(coverUrl = coverUrl) }
+
     suspend fun setStatus(id: Long, status: WatchStatus) = updateItem(id) { it.copy(status = status) }
 
     /** Marks one unit (episode/chapter) watched or not, by its (segment, unit) number. */

android/app/src/main/java/com/umt/tracker/ui/UmtNavHost.kt

@@ -1,5 +1,6 @@
 package com.umt.tracker.ui
 
+import android.net.Uri
 import androidx.compose.runtime.Composable
 import androidx.navigation.NavType
 import androidx.navigation.compose.NavHost
@@ -18,12 +19,14 @@ private object Routes {
     const val LIBRARY = "library"
     const val DETAIL = "detail/{itemId}"
     const val EDIT = "edit?itemId={itemId}"
-    const val SEARCH = "search/{type}"
+    const val SEARCH = "search/{type}?coverFor={coverFor}&q={q}"
     const val SETTINGS = "settings"
     const val STATS = "stats"
     fun detail(id: Long) = "detail/$id"
     fun edit(id: Long = 0) = "edit?itemId=$id"
-    fun search(type: MediaType) = "search/${type.name}"
+    fun search(type: MediaType) = "search/${type.name}?coverFor=0&q="
+    fun changeCover(type: MediaType, itemId: Long, title: String) =
+        "search/${type.name}?coverFor=$itemId&q=${Uri.encode(title)}"
 }
 
 @Composable
@@ -54,6 +57,9 @@ fun UmtNavHost() {
                 itemId = id,
                 onBack = { navController.popBackStack() },
                 onEdit = { navController.navigate(Routes.edit(id)) },
+                onChangeCover = { type, title ->
+                    navController.navigate(Routes.changeCover(type, id, title))
+                },
                 onDeleted = { navController.popBackStack() },
             )
         }
@@ -71,17 +77,31 @@ fun UmtNavHost() {
         }
         composable(
             route = Routes.SEARCH,
-            arguments = listOf(navArgument("type") { type = NavType.StringType }),
+            arguments = listOf(
+                navArgument("type") { type = NavType.StringType },
+                navArgument("coverFor") { type = NavType.LongType; defaultValue = 0L },
+                navArgument("q") { type = NavType.StringType; defaultValue = "" },
+            ),
         ) { backStackEntry ->
-            val typeName = backStackEntry.arguments?.getString("type") ?: MediaType.MOVIE.name
+            val args = backStackEntry.arguments
+            val typeName = args?.getString("type") ?: MediaType.MOVIE.name
             val type = runCatching { MediaType.valueOf(typeName) }.getOrDefault(MediaType.MOVIE)
+            val coverFor = args?.getLong("coverFor") ?: 0L
+            val query = args?.getString("q").orEmpty()
             SearchScreen(
                 type = type,
+                initialQuery = query,
+                coverForItemId = coverFor,
                 onBack = { navController.popBackStack() },
                 onPicked = {
-                    // Replace the current edit (if any) with a fresh, draft-filled one.
-                    navController.navigate(Routes.edit()) {
-                        popUpTo(Routes.EDIT) { inclusive = true }
+                    if (coverFor > 0) {
+                        // Cover-only change: just return to the detail screen.
+                        navController.popBackStack()
+                    } else {
+                        // Replace the current edit (if any) with a fresh, draft-filled one.
+                        navController.navigate(Routes.edit()) {
+                            popUpTo(Routes.EDIT) { inclusive = true }
+                        }
                     }
                 },
             )

android/app/src/main/java/com/umt/tracker/ui/detail/DetailScreen.kt

@@ -25,6 +25,7 @@ import androidx.compose.material.icons.filled.ExpandLess
 import androidx.compose.material.icons.filled.ExpandMore
 import androidx.compose.material.icons.filled.Favorite
 import androidx.compose.material.icons.filled.FavoriteBorder
+import androidx.compose.material.icons.filled.Image
 import androidx.compose.material.icons.filled.RadioButtonUnchecked
 import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.ExperimentalMaterial3Api
@@ -54,6 +55,7 @@ import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
 import coil.compose.AsyncImage
 import com.umt.tracker.domain.MediaItem
+import com.umt.tracker.domain.MediaType
 import com.umt.tracker.domain.Segment
 import com.umt.tracker.domain.WatchStatus
 import com.umt.tracker.domain.accentArgb
@@ -71,6 +73,7 @@ fun DetailScreen(
     itemId: Long,
     onBack: () -> Unit,
     onEdit: () -> Unit,
+    onChangeCover: (MediaType, String) -> Unit,
     onDeleted: () -> Unit,
     viewModel: DetailViewModel = viewModel(factory = DetailViewModel.factory(itemId)),
 ) {
@@ -115,7 +118,12 @@ fun DetailScreen(
                 Text("Nicht gefunden", color = MaterialTheme.colorScheme.onSurfaceVariant)
             }
         } else {
-            DetailContent(current, viewModel, Modifier.padding(padding))
+            DetailContent(
+                item = current,
+                viewModel = viewModel,
+                onChangeCover = { onChangeCover(current.type, current.title) },
+                modifier = Modifier.padding(padding),
+            )
         }
     }
 
@@ -141,6 +149,7 @@ fun DetailScreen(
 private fun DetailContent(
     item: MediaItem,
     viewModel: DetailViewModel,
+    onChangeCover: () -> Unit,
     modifier: Modifier = Modifier,
 ) {
     // Seasons/volumes start collapsed for overview, mirroring the desktop app.
@@ -153,21 +162,38 @@ private fun DetailContent(
     ) {
         item {
             Row {
-                Box(
-                    modifier = Modifier
-                        .width(120.dp)
-                        .height(180.dp)
-                        .clip(RoundedCornerShape(12.dp))
-                        .background(MaterialTheme.colorScheme.surfaceVariant),
-                    contentAlignment = Alignment.Center,
-                ) {
-                    if (item.coverUrl.isNotBlank()) {
-                        AsyncImage(
-                            model = item.coverUrl,
-                            contentDescription = item.title,
-                            contentScale = ContentScale.Crop,
-                            modifier = Modifier.fillMaxSize(),
+                Column(horizontalAlignment = Alignment.CenterHorizontally) {
+                    Box(
+                        modifier = Modifier
+                            .width(120.dp)
+                            .height(180.dp)
+                            .clip(RoundedCornerShape(12.dp))
+                            .background(MaterialTheme.colorScheme.surfaceVariant)
+                            .clickable(onClick = onChangeCover),
+                        contentAlignment = Alignment.Center,
+                    ) {
+                        if (item.coverUrl.isNotBlank()) {
+                            AsyncImage(
+                                model = item.coverUrl,
+                                contentDescription = item.title,
+                                contentScale = ContentScale.Crop,
+                                modifier = Modifier.fillMaxSize(),
+                            )
+                        } else {
+                            Icon(
+                                Icons.Filled.Image,
+                                contentDescription = null,
+                                tint = MaterialTheme.colorScheme.onSurfaceVariant,
+                            )
+                        }
+                    }
+                    TextButton(onClick = onChangeCover) {
+                        Icon(
+                            Icons.Filled.Image,
+                            contentDescription = null,
+                            modifier = Modifier.size(18.dp),
                         )
+                        Text("Cover ändern", modifier = Modifier.padding(start = 6.dp))
                     }
                 }
                 Column(modifier = Modifier.padding(start = 16.dp)) {

android/app/src/main/java/com/umt/tracker/ui/search/SearchScreen.kt

@@ -51,14 +51,18 @@ fun SearchScreen(
     type: MediaType,
     onBack: () -> Unit,
     onPicked: () -> Unit,
-    viewModel: SearchViewModel = viewModel(factory = SearchViewModel.factory(type)),
+    initialQuery: String = "",
+    coverForItemId: Long = 0,
+    viewModel: SearchViewModel = viewModel(
+        factory = SearchViewModel.factory(type, initialQuery, coverForItemId),
+    ),
 ) {
     val state by viewModel.state.collectAsStateWithLifecycle()
 
     Scaffold(
         topBar = {
             TopAppBar(
-                title = { Text("${type.labelPlural} suchen") },
+                title = { Text(if (state.coverMode) "Cover ändern" else "${type.labelPlural} suchen") },
                 navigationIcon = {
                     IconButton(onClick = onBack) {
                         Icon(Icons.AutoMirrored.Filled.ArrowBack, contentDescription = "Zurück")

android/app/src/main/java/com/umt/tracker/ui/search/SearchViewModel.kt

@@ -4,6 +4,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.viewModelScope
 import com.umt.tracker.Graph
+import com.umt.tracker.data.LibraryRepository
 import com.umt.tracker.providers.ProviderManager
 import com.umt.tracker.providers.SearchOutcome
 import com.umt.tracker.providers.SearchResult
@@ -22,24 +23,40 @@ data class SearchUiState(
     val error: String? = null,
     val hint: String = "",
     val searched: Boolean = false,
+    /** When true, a chosen hit only replaces the cover of [coverForItemId]. */
+    val coverMode: Boolean = false,
 )
 
 /**
- * Drives the online metadata search for a single [MediaType]. On select it
- * enriches the chosen hit (e.g. TMDB series seasons), stashes the resulting draft
- * item in [Graph.editDraft], and hands its type back so navigation can open the
- * edit screen pre-filled.
+ * Drives the online metadata search for a single [MediaType]. In the default
+ * (add) mode a chosen hit is enriched (e.g. TMDB series seasons), stashed as a
+ * draft in [Graph.editDraft], and the edit screen opens pre-filled. In cover mode
+ * ([coverForItemId] > 0) only the chosen hit's cover URL is applied to that
+ * existing item — mirroring the desktop "Cover ändern…" action.
  */
 class SearchViewModel(
     private val providers: ProviderManager,
+    private val repo: LibraryRepository,
     type: MediaType,
+    initialQuery: String,
+    private val coverForItemId: Long,
 ) : ViewModel() {
 
     private val _state = MutableStateFlow(
-        SearchUiState(type = type, hint = if (providers.isConfigured(type)) "" else providers.configHint(type)),
+        SearchUiState(
+            type = type,
+            query = initialQuery,
+            hint = if (providers.isConfigured(type)) "" else providers.configHint(type),
+            coverMode = coverForItemId > 0,
+        ),
     )
     val state: StateFlow<SearchUiState> = _state.asStateFlow()
 
+    init {
+        // Pre-filled title (cover mode) searches immediately, like the desktop dialog.
+        if (initialQuery.isNotBlank()) search()
+    }
+
     fun onQueryChange(value: String) {
         _state.value = _state.value.copy(query = value)
     }
@@ -58,22 +75,34 @@ class SearchViewModel(
         }
     }
 
-    /** Enriches and stages the chosen result; invokes [onReady] with its id (0 = new). */
+    /**
+     * Applies the chosen result: in cover mode it replaces the existing item's
+     * cover; otherwise it enriches and stages a draft for the edit screen. Invokes
+     * [onReady] once done.
+     */
     fun choose(result: SearchResult, onReady: () -> Unit) {
         _state.value = _state.value.copy(loading = true)
         viewModelScope.launch {
-            val full = providers.fetchDetails(result)
-            Graph.editDraft = full.toMediaItem()
+            if (coverForItemId > 0) {
+                repo.setCover(coverForItemId, result.coverUrl)
+            } else {
+                val full = providers.fetchDetails(result)
+                Graph.editDraft = full.toMediaItem()
+            }
             _state.value = _state.value.copy(loading = false)
             onReady()
         }
     }
 
     companion object {
-        fun factory(type: MediaType) = object : ViewModelProvider.Factory {
+        fun factory(
+            type: MediaType,
+            initialQuery: String = "",
+            coverForItemId: Long = 0,
+        ) = object : ViewModelProvider.Factory {
             @Suppress("UNCHECKED_CAST")
             override fun <T : ViewModel> create(modelClass: Class<T>): T =
-                SearchViewModel(Graph.providers, type) as T
+                SearchViewModel(Graph.providers, Graph.repository, type, initialQuery, coverForItemId) as T
         }
     }
 }