i18n: extract hardcoded strings into l10n keys

Move hardcoded UI strings across multiple screens and the notification
service into ARB-backed l10n keys so they can be translated via Crowdin.
Adds 62 new keys covering sort labels, dialog copy, metadata error
snackbars, folder-picker errors, home-tab error states, extensions home
feed selector, and all notification titles/bodies. NotificationService
now caches an AppLocalizations instance (injected from MainShell via
didChangeDependencies) and falls back to English literals when no locale
is available.

lib/screens/home_tab.dart

@@ -3124,7 +3124,7 @@ class _HomeTabState extends ConsumerState<HomeTab>
             Padding(
               padding: const EdgeInsets.only(right: 8),
               child: FilterChip(
-                label: const Text('All'),
+                label: Text(context.l10n.historyFilterAll),
                 selected: selectedFilter == null,
                 onSelected: (_) {
                   ref.read(trackProvider.notifier).setSearchFilter(null);
@@ -4212,7 +4212,7 @@ class _ExtensionAlbumScreenState extends ConsumerState<ExtensionAlbumScreen> {
 
       if (result == null) {
         setState(() {
-          _error = 'Failed to load album';
+          _error = context.l10n.errorLoadAlbum;
           _isLoading = false;
         });
         return;
@@ -4221,7 +4221,7 @@ class _ExtensionAlbumScreenState extends ConsumerState<ExtensionAlbumScreen> {
       final trackList = result['tracks'] as List<dynamic>?;
       if (trackList == null) {
         setState(() {
-          _error = 'No tracks found';
+          _error = context.l10n.errorNoTracksFound;
           _isLoading = false;
         });
         return;
@@ -4243,7 +4243,7 @@ class _ExtensionAlbumScreenState extends ConsumerState<ExtensionAlbumScreen> {
     } catch (e) {
       if (!mounted) return;
       setState(() {
-        _error = 'Error: $e';
+        _error = context.l10n.snackbarError(e.toString());
         _isLoading = false;
       });
     }
@@ -4376,7 +4376,7 @@ class _ExtensionPlaylistScreenState
 
       if (result == null) {
         setState(() {
-          _error = 'Failed to load playlist';
+          _error = context.l10n.errorLoadPlaylist;
           _isLoading = false;
         });
         return;
@@ -4385,7 +4385,7 @@ class _ExtensionPlaylistScreenState
       final trackList = result['tracks'] as List<dynamic>?;
       if (trackList == null) {
         setState(() {
-          _error = 'No tracks found';
+          _error = context.l10n.errorNoTracksFound;
           _isLoading = false;
         });
         return;
@@ -4402,7 +4402,7 @@ class _ExtensionPlaylistScreenState
     } catch (e) {
       if (!mounted) return;
       setState(() {
-        _error = 'Error: $e';
+        _error = context.l10n.snackbarError(e.toString());
         _isLoading = false;
       });
     }
@@ -4528,7 +4528,7 @@ class _ExtensionArtistScreenState extends ConsumerState<ExtensionArtistScreen> {
 
       if (result == null) {
         setState(() {
-          _error = 'Failed to load artist';
+          _error = context.l10n.errorLoadArtist;
           _isLoading = false;
         });
         return;
@@ -4562,7 +4562,7 @@ class _ExtensionArtistScreenState extends ConsumerState<ExtensionArtistScreen> {
     } catch (e) {
       if (!mounted) return;
       setState(() {
-        _error = 'Error: $e';
+        _error = context.l10n.snackbarError(e.toString());
         _isLoading = false;
       });
     }

lib/screens/main_shell.dart

@@ -18,6 +18,7 @@ import 'package:spotiflac_android/screens/settings/settings_tab.dart';
 import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/services/shell_navigation_service.dart';
 import 'package:spotiflac_android/services/share_intent_service.dart';
+import 'package:spotiflac_android/services/notification_service.dart';
 import 'package:spotiflac_android/services/update_checker.dart';
 import 'package:spotiflac_android/widgets/update_dialog.dart';
 import 'package:spotiflac_android/widgets/animation_utils.dart';
@@ -47,6 +48,12 @@ class _MainShellState extends ConsumerState<MainShell>
   final GlobalKey<NavigatorState> _repoTabNavigatorKey =
       ShellNavigationService.repoTabNavigatorKey;
 
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    NotificationService().updateStrings(context.l10n);
+  }
+
   @override
   void initState() {
     super.initState();

lib/screens/queue_tab.dart

@@ -2174,13 +2174,13 @@ class _QueueTabState extends ConsumerState<QueueTab> {
                                 ),
                               ),
                               FilterChip(
-                                label: const Text('A-Z'),
+                                label: Text(context.l10n.sortAlphaAsc),
                                 selected: tempSortMode == 'a-z',
                                 onSelected: (_) =>
                                     setSheetState(() => tempSortMode = 'a-z'),
                               ),
                               FilterChip(
-                                label: const Text('Z-A'),
+                                label: Text(context.l10n.sortAlphaDesc),
                                 selected: tempSortMode == 'z-a',
                                 onSelected: (_) =>
                                     setSheetState(() => tempSortMode = 'z-a'),
@@ -5461,18 +5461,18 @@ class _QueueTabState extends ConsumerState<QueueTab> {
               return await showDialog<bool>(
                     context: context,
                     builder: (ctx) => AlertDialog(
-                      title: const Text('Cancel download?'),
+                      title: Text(context.l10n.cancelDownloadTitle),
                       content: Text(
-                        'This will cancel the active download for "${item.track.name}".',
+                        context.l10n.cancelDownloadContent(item.track.name),
                       ),
                       actions: [
                         TextButton(
                           onPressed: () => Navigator.of(ctx).pop(false),
-                          child: const Text('Keep'),
+                          child: Text(context.l10n.cancelDownloadKeep),
                         ),
                         TextButton(
                           onPressed: () => Navigator.of(ctx).pop(true),
-                          child: const Text('Cancel'),
+                          child: Text(context.l10n.dialogCancel),
                         ),
                       ],
                     ),

lib/screens/settings/download_settings_page.dart

@@ -1359,7 +1359,9 @@ class _DownloadSettingsPageState extends ConsumerState<DownloadSettingsPage> {
                   if (ctx.mounted) {
                     ScaffoldMessenger.of(ctx).showSnackBar(
                       SnackBar(
-                        content: Text('Failed to open folder picker: $e'),
+                        content: Text(
+                          ctx.l10n.snackbarFolderPickerFailed(e.toString()),
+                        ),
                         backgroundColor: Theme.of(ctx).colorScheme.error,
                         duration: const Duration(seconds: 4),
                       ),

lib/screens/settings/extensions_page.dart

@@ -735,7 +735,7 @@ class _SearchProviderSelector extends ConsumerWidget {
                 (entry) => ListTile(
                   leading: Icon(Icons.search, color: colorScheme.tertiary),
                   title: Text(entry.value),
-                  subtitle: Text('Search with ${entry.value}'),
+                  subtitle: Text(ctx.l10n.extensionsSearchWith(entry.value)),
                   trailing: settings.searchProvider == entry.key
                       ? Icon(Icons.check_circle, color: colorScheme.primary)
                       : Icon(Icons.circle_outlined, color: colorScheme.outline),
@@ -791,7 +791,7 @@ class _HomeFeedProviderSelector extends ConsumerWidget {
 
     final hasAnyProvider = homeFeedProviders.isNotEmpty;
 
-    String currentProviderName = 'Auto';
+    String currentProviderName = context.l10n.extensionsHomeFeedAuto;
     if (settings.homeFeedProvider != null &&
         settings.homeFeedProvider!.isNotEmpty) {
       final ext = homeFeedProviders
@@ -828,7 +828,7 @@ class _HomeFeedProviderSelector extends ConsumerWidget {
                     crossAxisAlignment: CrossAxisAlignment.start,
                     children: [
                       Text(
-                        'Home Feed Provider',
+                        context.l10n.extensionsHomeFeedProvider,
                         style: Theme.of(context).textTheme.bodyLarge?.copyWith(
                           color: !hasAnyProvider ? colorScheme.outline : null,
                         ),
@@ -836,7 +836,7 @@ class _HomeFeedProviderSelector extends ConsumerWidget {
                       const SizedBox(height: 2),
                       Text(
                         !hasAnyProvider
-                            ? 'No extensions with home feed'
+                            ? context.l10n.extensionsNoHomeFeedExtensions
                             : currentProviderName,
                         style: Theme.of(context).textTheme.bodySmall?.copyWith(
                           color: colorScheme.onSurfaceVariant,
@@ -883,7 +883,7 @@ class _HomeFeedProviderSelector extends ConsumerWidget {
               Padding(
                 padding: const EdgeInsets.fromLTRB(24, 24, 24, 8),
                 child: Text(
-                  'Home Feed Provider',
+                  ctx.l10n.extensionsHomeFeedProvider,
                   style: Theme.of(
                     context,
                   ).textTheme.titleLarge?.copyWith(fontWeight: FontWeight.bold),
@@ -892,7 +892,7 @@ class _HomeFeedProviderSelector extends ConsumerWidget {
               Padding(
                 padding: const EdgeInsets.fromLTRB(24, 0, 24, 16),
                 child: Text(
-                  'Choose which extension provides the home feed on the main screen',
+                  ctx.l10n.extensionsHomeFeedDescription,
                   style: Theme.of(context).textTheme.bodyMedium?.copyWith(
                     color: colorScheme.onSurfaceVariant,
                   ),
@@ -900,8 +900,8 @@ class _HomeFeedProviderSelector extends ConsumerWidget {
               ),
               ListTile(
                 leading: Icon(Icons.auto_awesome, color: colorScheme.primary),
-                title: const Text('Auto'),
-                subtitle: const Text('Automatically select the best available'),
+                title: Text(ctx.l10n.extensionsHomeFeedAuto),
+                subtitle: Text(ctx.l10n.extensionsHomeFeedAutoSubtitle),
                 trailing:
                     (settings.homeFeedProvider == null ||
                         settings.homeFeedProvider!.isEmpty)
@@ -917,7 +917,9 @@ class _HomeFeedProviderSelector extends ConsumerWidget {
                 (ext) => ListTile(
                   leading: Icon(Icons.extension, color: colorScheme.secondary),
                   title: Text(ext.displayName),
-                  subtitle: Text('Use ${ext.displayName} home feed'),
+                  subtitle: Text(
+                    ctx.l10n.extensionsHomeFeedUse(ext.displayName),
+                  ),
                   trailing: settings.homeFeedProvider == ext.id
                       ? Icon(Icons.check_circle, color: colorScheme.primary)
                       : Icon(Icons.circle_outlined, color: colorScheme.outline),

lib/screens/settings/options_settings_page.dart

@@ -307,9 +307,9 @@ class OptionsSettingsPage extends ConsumerWidget {
     } catch (e) {
       if (context.mounted) {
         Navigator.pop(context); // Close loading dialog
-        ScaffoldMessenger.of(
-          context,
-        ).showSnackBar(SnackBar(content: Text('Error: $e')));
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(content: Text(context.l10n.snackbarError(e.toString()))),
+        );
       }
     }
   }

lib/screens/setup_screen.dart

@@ -339,7 +339,9 @@ class _SetupScreenState extends ConsumerState<SetupScreen> {
                   if (mounted) {
                     ScaffoldMessenger.of(context).showSnackBar(
                       SnackBar(
-                        content: Text('Failed to open folder picker: $e'),
+                        content: Text(
+                          context.l10n.snackbarFolderPickerFailed(e.toString()),
+                        ),
                         backgroundColor: Theme.of(context).colorScheme.error,
                         duration: const Duration(seconds: 4),
                       ),
@@ -430,9 +432,9 @@ class _SetupScreenState extends ConsumerState<SetupScreen> {
       if (mounted) context.go('/tutorial');
     } catch (e) {
       if (mounted) {
-        ScaffoldMessenger.of(
-          context,
-        ).showSnackBar(SnackBar(content: Text('Error: $e')));
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(content: Text(context.l10n.snackbarError(e.toString()))),
+        );
       }
     } finally {
       setState(() => _isLoading = false);

lib/screens/track_metadata_screen.dart

@@ -5025,9 +5025,7 @@ class _EditMetadataSheetState extends State<_EditMetadataSheet> {
         if (ffmpegResult == null) {
           if (mounted) {
             ScaffoldMessenger.of(context).showSnackBar(
-              const SnackBar(
-                content: Text('Failed to save metadata via FFmpeg'),
-              ),
+              SnackBar(content: Text(context.l10n.metadataSaveFailedFfmpeg)),
             );
           }
           setState(() => _saving = false);
@@ -5038,9 +5036,7 @@ class _EditMetadataSheetState extends State<_EditMetadataSheet> {
           final ok = await PlatformBridge.writeTempToSaf(ffmpegResult, safUri);
           if (!ok && mounted) {
             ScaffoldMessenger.of(context).showSnackBar(
-              const SnackBar(
-                content: Text('Failed to write metadata back to storage'),
-              ),
+              SnackBar(content: Text(context.l10n.metadataSaveFailedStorage)),
             );
             setState(() => _saving = false);
             return;
@@ -5094,7 +5090,7 @@ class _EditMetadataSheetState extends State<_EditMetadataSheet> {
                 children: [
                   Expanded(
                     child: Text(
-                      'Edit Metadata',
+                      context.l10n.trackEditMetadata,
                       style: Theme.of(context).textTheme.titleLarge?.copyWith(
                         fontWeight: FontWeight.bold,
                       ),
@@ -5107,7 +5103,10 @@ class _EditMetadataSheetState extends State<_EditMetadataSheet> {
                       child: CircularProgressIndicator(strokeWidth: 2),
                     )
                   else
-                    FilledButton(onPressed: _save, child: const Text('Save')),
+                    FilledButton(
+                      onPressed: _save,
+                      child: Text(context.l10n.dialogSave),
+                    ),
                 ],
               ),
             ),