feat(extension): add custom URL handler support for extensions

- Add URLHandlerConfig to extension manifest (Go)
- Add HandleURL method to extension providers (Go)
- Add export functions for URL handling (Go)
- Add URLHandler class to extension_provider.dart (Flutter)
- Add platform bridge methods for URL handling (Flutter)
- Update fetchFromUrl to check extension URL handlers first
- Add Android/iOS native handlers for extension URL routing
- Update CHANGELOG with new feature

lib/providers/extension_provider.dart

@@ -24,6 +24,7 @@ class Extension {
   final bool hasDownloadProvider;
   final bool skipMetadataEnrichment; // If true, use metadata from extension instead of enriching
   final SearchBehavior? searchBehavior; // Custom search behavior
+  final URLHandler? urlHandler; // Custom URL handling
   final TrackMatching? trackMatching; // Custom track matching
   final PostProcessing? postProcessing; // Post-processing hooks
 
@@ -45,6 +46,7 @@ class Extension {
     this.hasDownloadProvider = false,
     this.skipMetadataEnrichment = false,
     this.searchBehavior,
+    this.urlHandler,
     this.trackMatching,
     this.postProcessing,
   });
@@ -74,6 +76,9 @@ class Extension {
       searchBehavior: json['search_behavior'] != null 
           ? SearchBehavior.fromJson(json['search_behavior'] as Map<String, dynamic>)
           : null,
+      urlHandler: json['url_handler'] != null
+          ? URLHandler.fromJson(json['url_handler'] as Map<String, dynamic>)
+          : null,
       trackMatching: json['track_matching'] != null
           ? TrackMatching.fromJson(json['track_matching'] as Map<String, dynamic>)
           : null,
@@ -101,6 +106,7 @@ class Extension {
     bool? hasDownloadProvider,
     bool? skipMetadataEnrichment,
     SearchBehavior? searchBehavior,
+    URLHandler? urlHandler,
     TrackMatching? trackMatching,
     PostProcessing? postProcessing,
   }) {
@@ -122,12 +128,14 @@ class Extension {
       hasDownloadProvider: hasDownloadProvider ?? this.hasDownloadProvider,
       skipMetadataEnrichment: skipMetadataEnrichment ?? this.skipMetadataEnrichment,
       searchBehavior: searchBehavior ?? this.searchBehavior,
+      urlHandler: urlHandler ?? this.urlHandler,
       trackMatching: trackMatching ?? this.trackMatching,
       postProcessing: postProcessing ?? this.postProcessing,
     );
   }
 
   bool get hasCustomSearch => searchBehavior?.enabled ?? false;
+  bool get hasURLHandler => urlHandler?.enabled ?? false;
   bool get hasCustomMatching => trackMatching?.customMatching ?? false;
   bool get hasPostProcessing => postProcessing?.enabled ?? false;
 }
@@ -226,6 +234,36 @@ class PostProcessing {
   }
 }
 
+/// URL handler configuration for custom URL patterns
+class URLHandler {
+  final bool enabled;
+  final List<String> patterns;
+
+  const URLHandler({
+    required this.enabled,
+    this.patterns = const [],
+  });
+
+  factory URLHandler.fromJson(Map<String, dynamic> json) {
+    return URLHandler(
+      enabled: json['enabled'] as bool? ?? false,
+      patterns: (json['patterns'] as List<dynamic>?)?.cast<String>() ?? [],
+    );
+  }
+
+  /// Check if a URL matches any of the patterns
+  bool matchesURL(String url) {
+    if (!enabled || patterns.isEmpty) return false;
+    final lowerUrl = url.toLowerCase();
+    for (final pattern in patterns) {
+      if (lowerUrl.contains(pattern.toLowerCase())) {
+        return true;
+      }
+    }
+    return false;
+  }
+}
+
 /// A post-processing hook
 class PostProcessingHook {
   final String id;

lib/providers/track_provider.dart

@@ -131,6 +131,45 @@ class TrackNotifier extends Notifier<TrackState> {
     state = TrackState(isLoading: true, hasSearchText: state.hasSearchText);
 
     try {
+      // First, check if any extension can handle this URL
+      final extensionHandler = await PlatformBridge.findURLHandler(url);
+      if (extensionHandler != null) {
+        _log.i('Found extension URL handler: $extensionHandler for URL: $url');
+        final result = await PlatformBridge.handleURLWithExtension(url);
+        if (!_isRequestValid(requestId)) return;
+        
+        if (result != null) {
+          final type = result['type'] as String?;
+          final extensionId = result['extension_id'] as String?;
+          
+          if (type == 'track' && result['track'] != null) {
+            final trackData = result['track'] as Map<String, dynamic>;
+            final track = _parseSearchTrack(trackData, source: extensionId);
+            state = TrackState(
+              tracks: [track],
+              isLoading: false,
+              coverUrl: track.coverUrl,
+              searchExtensionId: extensionId,
+            );
+            return;
+          } else if ((type == 'album' || type == 'playlist') && result['tracks'] != null) {
+            final trackList = result['tracks'] as List<dynamic>;
+            final tracks = trackList.map((t) => _parseSearchTrack(t as Map<String, dynamic>, source: extensionId)).toList();
+            state = TrackState(
+              tracks: tracks,
+              isLoading: false,
+              albumId: result['album']?['id'] as String?,
+              albumName: result['name'] as String? ?? result['album']?['name'] as String?,
+              playlistName: type == 'playlist' ? result['name'] as String? : null,
+              coverUrl: result['cover_url'] as String?,
+              searchExtensionId: extensionId,
+            );
+            return;
+          }
+        }
+      }
+      
+      // No extension handler found, try Spotify URL parsing
       final parsed = await PlatformBridge.parseSpotifyUrl(url);
       if (!_isRequestValid(requestId)) return; // Request cancelled
       

lib/services/platform_bridge.dart

@@ -753,6 +753,40 @@ class PlatformBridge {
     return list.map((e) => e as Map<String, dynamic>).toList();
   }
 
+  // ==================== EXTENSION URL HANDLER ====================
+
+  /// Handle a URL with any matching extension
+  /// Returns null if no extension can handle the URL
+  static Future<Map<String, dynamic>?> handleURLWithExtension(String url) async {
+    try {
+      final result = await _channel.invokeMethod('handleURLWithExtension', {
+        'url': url,
+      });
+      if (result == null || result == '') return null;
+      return jsonDecode(result as String) as Map<String, dynamic>;
+    } catch (e) {
+      // No extension found or error handling URL
+      return null;
+    }
+  }
+
+  /// Find an extension that can handle the given URL
+  /// Returns extension ID or null if none found
+  static Future<String?> findURLHandler(String url) async {
+    final result = await _channel.invokeMethod('findURLHandler', {
+      'url': url,
+    });
+    if (result == null || result == '') return null;
+    return result as String;
+  }
+
+  /// Get all extensions that handle custom URLs
+  static Future<List<Map<String, dynamic>>> getURLHandlers() async {
+    final result = await _channel.invokeMethod('getURLHandlers');
+    final list = jsonDecode(result as String) as List<dynamic>;
+    return list.map((e) => e as Map<String, dynamic>).toList();
+  }
+
   // ==================== EXTENSION POST-PROCESSING ====================
 
   /// Run post-processing hooks on a file