feat: add lyrics source tracking, Paxsenix partner, and dedicated lyrics provider settings page

- Add getLyricsLRCWithSource to return lyrics with source metadata
- Display lyrics source in track metadata screen
- Improve LRC parsing to preserve background vocal tags
- Add dedicated LyricsProviderPriorityPage for provider configuration
- Add Paxsenix as lyrics proxy partner for Apple Music/QQ Music
- Handle inline timestamps and speaker prefixes in LRC display

lib/services/platform_bridge.dart

@@ -276,6 +276,23 @@ class PlatformBridge {
     return result as String;
   }
 
+  static Future<Map<String, dynamic>> getLyricsLRCWithSource(
+    String spotifyId,
+    String trackName,
+    String artistName, {
+    String? filePath,
+    int durationMs = 0,
+  }) async {
+    final result = await _channel.invokeMethod('getLyricsLRCWithSource', {
+      'spotify_id': spotifyId,
+      'track_name': trackName,
+      'artist_name': artistName,
+      'file_path': filePath ?? '',
+      'duration_ms': durationMs,
+    });
+    return jsonDecode(result as String) as Map<String, dynamic>;
+  }
+
   static Future<Map<String, dynamic>> embedLyricsToFile(
     String filePath,
     String lyrics,
@@ -350,14 +367,17 @@ class PlatformBridge {
   }
 
   /// Returns metadata about all available lyrics providers.
-  static Future<List<Map<String, dynamic>>> getAvailableLyricsProviders() async {
+  static Future<List<Map<String, dynamic>>>
+  getAvailableLyricsProviders() async {
     final result = await _channel.invokeMethod('getAvailableLyricsProviders');
     final List<dynamic> decoded = jsonDecode(result as String) as List<dynamic>;
     return decoded.cast<Map<String, dynamic>>();
   }
 
   /// Sets advanced lyrics fetch options used by provider-specific integrations.
-  static Future<void> setLyricsFetchOptions(Map<String, dynamic> options) async {
+  static Future<void> setLyricsFetchOptions(
+    Map<String, dynamic> options,
+  ) async {
     final optionsJSON = jsonEncode(options);
     await _channel.invokeMethod('setLyricsFetchOptions', {
       'options_json': optionsJSON,