refactor: remove built-in Spotify API provider, use Deezer as sole default

- Remove all Spotify credential management (client ID/secret, secure storage)
- Remove Spotify platform channel handlers from MainActivity
- Remove exported Go functions: GetSpotifyMetadata, SearchSpotify,
  SearchSpotifyAll, GetSpotifyRelatedArtists, SetSpotifyAPICredentials
- Simplify GetSpotifyMetadataWithDeezerFallback to SpotFetch-only path
- Remove Spotify built-in fallback in ReEnrichFile search pipeline
- Always return false from HasSpotifyCredentials; getCredentials always errors
- Default metadataProviderPriority is now ['deezer'] only
- Sanitize provider priority list to strip 'spotify' entries on load/save
- Add migration v5 to clear saved Spotify credentials from existing installs
- Remove Spotify source chip and credentials UI from options settings page
- Remove metadataSource param from search() — always uses Deezer
- spotify-web extension remains supported via the extension provider system

lib/providers/extension_provider.dart

@@ -823,11 +823,19 @@ class ExtensionNotifier extends Notifier<ExtensionState> {
       List<String> priority;
       if (savedJson != null) {
         final saved = jsonDecode(savedJson) as List<dynamic>;
-        priority = saved.map((e) => e as String).toList();
+        priority = _sanitizeMetadataProviderPriority(
+          saved.map((e) => e as String).toList(),
+        );
         _log.d('Loaded metadata provider priority from prefs: $priority');
+        await prefs.setString(
+          _metadataProviderPriorityKey,
+          jsonEncode(priority),
+        );
         await PlatformBridge.setMetadataProviderPriority(priority);
       } else {
-        priority = await PlatformBridge.getMetadataProviderPriority();
+        priority = _sanitizeMetadataProviderPriority(
+          await PlatformBridge.getMetadataProviderPriority(),
+        );
         _log.d('Using default metadata provider priority: $priority');
       }
 
@@ -840,11 +848,15 @@ class ExtensionNotifier extends Notifier<ExtensionState> {
   Future<void> setMetadataProviderPriority(List<String> priority) async {
     try {
       final prefs = await SharedPreferences.getInstance();
-      await prefs.setString(_metadataProviderPriorityKey, jsonEncode(priority));
+      final sanitized = _sanitizeMetadataProviderPriority(priority);
+      await prefs.setString(
+        _metadataProviderPriorityKey,
+        jsonEncode(sanitized),
+      );
 
-      await PlatformBridge.setMetadataProviderPriority(priority);
-      state = state.copyWith(metadataProviderPriority: priority);
-      _log.d('Saved metadata provider priority: $priority');
+      await PlatformBridge.setMetadataProviderPriority(sanitized);
+      state = state.copyWith(metadataProviderPriority: sanitized);
+      _log.d('Saved metadata provider priority: $sanitized');
     } catch (e) {
       _log.e('Failed to set metadata provider priority: $e');
       state = state.copyWith(error: e.toString());
@@ -880,7 +892,7 @@ class ExtensionNotifier extends Notifier<ExtensionState> {
   }
 
   List<String> getAllMetadataProviders() {
-    final providers = ['deezer', 'spotify'];
+    final providers = ['deezer'];
     for (final ext in state.extensions) {
       if (ext.enabled && ext.hasMetadataProvider) {
         providers.add(ext.id);
@@ -889,6 +901,23 @@ class ExtensionNotifier extends Notifier<ExtensionState> {
     return providers;
   }
 
+  List<String> _sanitizeMetadataProviderPriority(List<String> input) {
+    final allowed = getAllMetadataProviders().toSet();
+    final result = <String>[];
+
+    for (final provider in input) {
+      if (allowed.contains(provider) && !result.contains(provider)) {
+        result.add(provider);
+      }
+    }
+
+    if (!result.contains('deezer')) {
+      result.insert(0, 'deezer');
+    }
+
+    return result;
+  }
+
   List<Extension> get searchProviders {
     return state.extensions
         .where((ext) => ext.enabled && ext.hasCustomSearch)

lib/providers/settings_provider.dart

@@ -9,7 +9,7 @@ import 'package:spotiflac_android/utils/logger.dart';
 
 const _settingsKey = 'app_settings';
 const _migrationVersionKey = 'settings_migration_version';
-const _currentMigrationVersion = 4;
+const _currentMigrationVersion = 5;
 const _spotifyClientSecretKey = 'spotify_client_secret';
 final _log = AppLogger('SettingsProvider');
 
@@ -41,9 +41,7 @@ class SettingsNotifier extends Notifier<AppSettings> {
       await _normalizeSongLinkRegionIfNeeded();
     }
 
-    await _loadSpotifyClientSecret(prefs);
-
-    _applySpotifyCredentials();
+    await _retireBuiltInSpotifyProvider();
 
     LogBuffer.loggingEnabled = state.enableLogging;
 
@@ -105,6 +103,17 @@ class SettingsNotifier extends Notifier<AppSettings> {
         }
         state = state.copyWith(lyricsProviders: updatedProviders);
       }
+      if (state.metadataSource != 'deezer' ||
+          state.spotifyClientId.isNotEmpty ||
+          state.spotifyClientSecret.isNotEmpty ||
+          state.useCustomSpotifyCredentials) {
+        state = state.copyWith(
+          metadataSource: 'deezer',
+          spotifyClientId: '',
+          spotifyClientSecret: '',
+          useCustomSpotifyCredentials: false,
+        );
+      }
       state = state.copyWith(lastSeenVersion: AppInfo.version);
       await prefs.setInt(_migrationVersionKey, _currentMigrationVersion);
       await _saveSettings();
@@ -193,49 +202,28 @@ class SettingsNotifier extends Notifier<AppSettings> {
     await _saveSettings();
   }
 
-  Future<void> _loadSpotifyClientSecret(SharedPreferences prefs) async {
+  Future<void> _retireBuiltInSpotifyProvider() async {
     final storedSecret = await _secureStorage.read(
       key: _spotifyClientSecretKey,
     );
-    final prefsSecret = state.spotifyClientSecret;
-
-    if ((storedSecret == null || storedSecret.isEmpty) &&
-        prefsSecret.isNotEmpty) {
-      await _secureStorage.write(
-        key: _spotifyClientSecretKey,
-        value: prefsSecret,
-      );
-    }
-
-    final effectiveSecret = (storedSecret != null && storedSecret.isNotEmpty)
-        ? storedSecret
-        : (prefsSecret.isNotEmpty ? prefsSecret : '');
-
-    if (effectiveSecret != state.spotifyClientSecret) {
-      state = state.copyWith(spotifyClientSecret: effectiveSecret);
-    }
-
-    if (prefsSecret.isNotEmpty) {
-      await _saveSettings();
-    }
-  }
-
-  Future<void> _storeSpotifyClientSecret(String secret) async {
-    if (secret.isEmpty) {
+    if (storedSecret != null && storedSecret.isNotEmpty) {
       await _secureStorage.delete(key: _spotifyClientSecretKey);
-    } else {
-      await _secureStorage.write(key: _spotifyClientSecretKey, value: secret);
     }
-  }
 
-  Future<void> _applySpotifyCredentials() async {
-    if (state.spotifyClientId.isNotEmpty &&
-        state.spotifyClientSecret.isNotEmpty) {
-      await PlatformBridge.setSpotifyCredentials(
-        state.spotifyClientId,
-        state.spotifyClientSecret,
-      );
+    if (state.metadataSource == 'deezer' &&
+        state.spotifyClientId.isEmpty &&
+        state.spotifyClientSecret.isEmpty &&
+        !state.useCustomSpotifyCredentials) {
+      return;
     }
+
+    state = state.copyWith(
+      metadataSource: 'deezer',
+      spotifyClientId: '',
+      spotifyClientSecret: '',
+      useCustomSpotifyCredentials: false,
+    );
+    await _saveSettings();
   }
 
   void setDefaultService(String service) {
@@ -396,45 +384,9 @@ class SettingsNotifier extends Notifier<AppSettings> {
     _saveSettings();
   }
 
-  void setSpotifyClientId(String clientId) {
-    state = state.copyWith(spotifyClientId: clientId);
-    _saveSettings();
-  }
-
-  Future<void> setSpotifyClientSecret(String clientSecret) async {
-    state = state.copyWith(spotifyClientSecret: clientSecret);
-    await _storeSpotifyClientSecret(clientSecret);
-    _saveSettings();
-  }
-
-  Future<void> setSpotifyCredentials(
-    String clientId,
-    String clientSecret,
-  ) async {
-    state = state.copyWith(
-      spotifyClientId: clientId,
-      spotifyClientSecret: clientSecret,
-    );
-    await _storeSpotifyClientSecret(clientSecret);
-    _saveSettings();
-    _applySpotifyCredentials();
-  }
-
-  Future<void> clearSpotifyCredentials() async {
-    state = state.copyWith(spotifyClientId: '', spotifyClientSecret: '');
-    await _storeSpotifyClientSecret('');
-    _saveSettings();
-    _applySpotifyCredentials();
-  }
-
-  void setUseCustomSpotifyCredentials(bool enabled) {
-    state = state.copyWith(useCustomSpotifyCredentials: enabled);
-    _saveSettings();
-    _applySpotifyCredentials();
-  }
-
   void setMetadataSource(String source) {
-    state = state.copyWith(metadataSource: source);
+    final normalized = source == 'deezer' ? 'deezer' : 'deezer';
+    state = state.copyWith(metadataSource: normalized);
     _saveSettings();
   }
 

lib/providers/track_provider.dart

@@ -458,7 +458,8 @@ class TrackNotifier extends Notifier<TrackState> {
       }
 
       // If URL doesn't match any known service, it's unrecognized
-      final isSpotifyUrl = url.contains('open.spotify.com') ||
+      final isSpotifyUrl =
+          url.contains('open.spotify.com') ||
           url.contains('spotify.link') ||
           url.startsWith('spotify:');
       if (!isSpotifyUrl) {
@@ -546,11 +547,7 @@ class TrackNotifier extends Notifier<TrackState> {
     }
   }
 
-  Future<void> search(
-    String query, {
-    String? metadataSource,
-    String? filterOverride,
-  }) async {
+  Future<void> search(String query, {String? filterOverride}) async {
     final requestId = ++_currentRequestId;
 
     // Preserve selected filter during loading
@@ -576,7 +573,7 @@ class TrackNotifier extends Notifier<TrackState> {
           searchProvider != null &&
           searchProvider.isNotEmpty;
 
-      final source = metadataSource ?? 'deezer';
+      const source = 'deezer';
 
       _log.i(
         'Search started: source=$source, query="$query", useExtensions=$useExtensions, filter=$currentFilter',
@@ -602,32 +599,20 @@ class TrackNotifier extends Notifier<TrackState> {
             }
           }
         } catch (e) {
-          _log.w('Extension search failed, falling back to built-in: $e');
+          _log.w('Extension search failed, falling back to Deezer: $e');
         }
       }
 
-      if (source == 'deezer') {
-        _log.d('Calling Deezer search API...');
-        results = await PlatformBridge.searchDeezerAll(
-          query,
-          trackLimit: 20,
-          artistLimit: 2,
-          filter: currentFilter,
-        );
-        _log.i(
-          'Deezer returned ${(results['tracks'] as List?)?.length ?? 0} tracks, ${(results['artists'] as List?)?.length ?? 0} artists, ${(results['albums'] as List?)?.length ?? 0} albums',
-        );
-      } else {
-        _log.d('Calling Spotify search API...');
-        results = await PlatformBridge.searchSpotifyAll(
-          query,
-          trackLimit: 20,
-          artistLimit: 2,
-        );
-        _log.i(
-          'Spotify returned ${(results['tracks'] as List?)?.length ?? 0} tracks, ${(results['artists'] as List?)?.length ?? 0} artists',
-        );
-      }
+      _log.d('Calling Deezer search API...');
+      results = await PlatformBridge.searchDeezerAll(
+        query,
+        trackLimit: 20,
+        artistLimit: 2,
+        filter: currentFilter,
+      );
+      _log.i(
+        'Deezer returned ${(results['tracks'] as List?)?.length ?? 0} tracks, ${(results['artists'] as List?)?.length ?? 0} artists, ${(results['albums'] as List?)?.length ?? 0} albums',
+      );
 
       if (!_isRequestValid(requestId)) {
         _log.w('Search request cancelled (requestId=$requestId)');