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/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;