feat: remove Tidal built-in provider, add extension download dedup/ISRC/Lyrics APIs, and expand l10n/a11y

Remove Tidal from built-in provider registry (metadata, search, download,
URL parsing) and delete tidal.go. Introduce extension runtime APIs for
lyrics lookup (getLyricsLRC), ISRC existence check (checkISRCExists), and
ISRC index management (addToISRCIndex). Refactor extension download response
construction into normalizeExtensionDownloadResult/overlayExtensionDownloadMetadata
helpers with AlreadyExists support and ISRC indexing. Switch download mirrors
to DoRequestWithUserAgent for ISP blocking detection. Add 50+ new
localization keys and accessibility labels across all supported locales.

lib/services/local_track_redownload_service.dart

@@ -108,7 +108,7 @@ class LocalTrackRedownloadService {
       case 'deezer':
         return settings.defaultService.toLowerCase();
       default:
-        return 'tidal';
+        return '';
     }
   }
 

lib/services/platform_bridge.dart

@@ -547,22 +547,6 @@ class PlatformBridge {
     return jsonDecode(result as String) as Map<String, dynamic>;
   }
 
-  static Future<Map<String, dynamic>> getTidalMetadata(
-    String resourceType,
-    String resourceId,
-  ) async {
-    final result = await _channel.invokeMethod('getTidalMetadata', {
-      'resource_type': resourceType,
-      'resource_id': resourceId,
-    });
-    if (result == null) {
-      throw Exception(
-        'getTidalMetadata returned null for $resourceType:$resourceId',
-      );
-    }
-    return jsonDecode(result as String) as Map<String, dynamic>;
-  }
-
   static Future<Map<String, dynamic>> getProviderMetadata(
     String providerId,
     String resourceType,
@@ -581,15 +565,6 @@ class PlatformBridge {
     return jsonDecode(result as String) as Map<String, dynamic>;
   }
 
-  static Future<Map<String, dynamic>> convertTidalToSpotifyDeezer(
-    String tidalUrl,
-  ) async {
-    final result = await _channel.invokeMethod('convertTidalToSpotifyDeezer', {
-      'url': tidalUrl,
-    });
-    return jsonDecode(result as String) as Map<String, dynamic>;
-  }
-
   static Future<Map<String, dynamic>> searchDeezerByISRC(
     String isrc, {
     String? itemId,