feat(player): notification favorite via MediaControl.custom (6c)

Adds a heart action to the media notification implemented as a custom
control + customAction handler — NOT setRating, which is broken
upstream (audio_service #376: onSetRating never fires from a
notification tap) and previously blanked the Pixel Watch.

- res/drawable/ic_stat_favorite{,_border}.xml: white 24dp vector hearts
- audio_handler: favorite MediaControl.custom in _broadcastState
  (icon/label toggle by LikeBridge state; kept out of
  androidCompactActionIndices so compact/lock + Wear transport are
  unchanged); customAction override (Future<dynamic>, matches base)
  toggles the like then re-broadcasts; refreshFavoriteControl()
- player_provider: cascade refreshFavoriteControl into the likedIds
  listener so liking from TrackRow/kebab/SSE flips the notification heart

Reliable on phone notification + lock screen; Wear/Auto display of a
non-transport custom action is platform-dependent (not a bug).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/android/app/src/main/res/drawable/ic_stat_favorite.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="#FFFFFFFF">
+  <path
+      android:fillColor="#FFFFFFFF"
+      android:pathData="M12,21.35l-1.45,-1.32C5.4,15.36 2,12.28 2,8.5 2,5.42 4.42,3 7.5,3c1.74,0 3.41,0.81 4.5,2.09C13.09,3.81 14.76,3 16.5,3 19.58,3 22,5.42 22,8.5c0,3.78 -3.4,6.86 -8.55,11.54L12,21.35z"/>
+</vector>

flutter_client/android/app/src/main/res/drawable/ic_stat_favorite_border.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="#FFFFFFFF">
+  <path
+      android:fillColor="#FFFFFFFF"
+      android:pathData="M16.5,3c-1.74,0 -3.41,0.81 -4.5,2.09C10.91,3.81 9.24,3 7.5,3 4.42,3 2,5.42 2,8.5c0,3.78 3.4,6.86 8.55,11.54L12,21.35l1.45,-1.32C18.6,15.36 22,12.28 22,8.5 22,5.42 19.58,3 16.5,3zM12.1,18.55l-0.1,0.1 -0.1,-0.1C7.14,14.24 4,11.39 4,8.5 4,6.5 5.5,5 7.5,5c1.54,0 3.04,0.99 3.57,2.36h1.87C13.46,5.99 14.96,5 16.5,5c2,0 3.5,1.5 3.5,3.5 0,2.89 -3.14,5.74 -7.9,10.05z"/>
+</vector>

flutter_client/lib/player/audio_handler.dart

@@ -637,6 +637,12 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
     mediaItem.add(media.copyWith(rating: Rating.newHeartRating(liked)));
   }
 
+  /// Re-broadcasts PlaybackState so the notification favorite control's
+  /// icon/label reflects a like toggled from elsewhere (TrackRow, kebab,
+  /// another device via SSE). Sibling to refreshCurrentRating, which
+  /// updates the Wear/lock heart via MediaItem.rating.
+  void refreshFavoriteControl() => _broadcastState(null);
+
   @override
   Future<void> setShuffleMode(AudioServiceShuffleMode shuffleMode) async {
     await _player
@@ -661,16 +667,56 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
     await _player.setVolume(v.clamp(0.0, 1.0));
   }
 
+  /// Handles the notification favorite control (and any future custom
+  /// actions). Toggles the current track's like via the LikeBridge,
+  /// then re-broadcasts so the heart icon/label flips. Signature
+  /// matches AudioHandler.customAction (Future<dynamic>).
+  @override
+  Future<dynamic> customAction(String name,
+      [Map<String, dynamic>? extras]) async {
+    if (name == 'minstrel.favorite') {
+      final media = mediaItem.value;
+      final bridge = _likeBridge;
+      if (media == null || bridge == null) return null;
+      try {
+        await bridge.toggleTrackLike(media.id);
+      } catch (_) {}
+      _broadcastState(null);
+      return null;
+    }
+    return super.customAction(name, extras);
+  }
+
   // _broadcastState accepts a nullable event because the shuffle/repeat
   // listeners don't have one — we just want to re-emit PlaybackState
   // with up-to-date shuffleMode/repeatMode fields.
   void _broadcastState(PlaybackEvent? event) {
     final playing = _player.playing;
+    // Favorite control: only when a track is playing and the LikeBridge
+    // is wired. Icon/label toggle by current like state; tapping it
+    // routes to customAction('minstrel.favorite'). Implemented as a
+    // MediaControl.custom (NOT setRating — that path is broken upstream,
+    // audio_service #376, and regressed the Pixel Watch). Kept out of
+    // androidCompactActionIndices so the compact/lock view is unchanged.
+    final favTrackId = mediaItem.value?.id;
+    final favBridge = _likeBridge;
+    final showFav = favTrackId != null && favBridge != null;
+    final favLiked = favTrackId != null &&
+        favBridge != null &&
+        favBridge.isTrackLiked(favTrackId);
     playbackState.add(PlaybackState(
       controls: [
         MediaControl.skipToPrevious,
         if (playing) MediaControl.pause else MediaControl.play,
         MediaControl.skipToNext,
+        if (showFav)
+          MediaControl.custom(
+            androidIcon: favLiked
+                ? 'drawable/ic_stat_favorite'
+                : 'drawable/ic_stat_favorite_border',
+            label: favLiked ? 'Unfavorite' : 'Favorite',
+            name: 'minstrel.favorite',
+          ),
       ],
       // androidCompactActionIndices tells the system which controls
       // appear in the collapsed/lock-screen view. Without this, some

flutter_client/lib/player/player_provider.dart

@@ -62,7 +62,9 @@ class PlayerActions {
     // kebab menu, or another logged-in device propagating via SSE.
     _ref.listen<AsyncValue<LikedIds>>(likedIdsProvider, (_, next) {
       if (next.value == null) return;
-      _ref.read(audioHandlerProvider).refreshCurrentRating();
+      _ref.read(audioHandlerProvider)
+        ..refreshCurrentRating()
+        ..refreshFavoriteControl();
     });
   }
   final Ref _ref;