fix(player): remove custom favorite MediaControl — it killed the notification

Device logcat (Pixel 6 Pro / Android 16) showed audio_service throwing
on every state broadcast:

  java.lang.IllegalArgumentException: You must specify an icon resource
  id to build a CustomAction
    at com.ryanheise.audioservice.AudioService...

The #57 MediaControl.custom favorite makes audio_service build a
PlaybackStateCompat.CustomAction whose icon id resolves to 0 on real
builds; the exception aborts the ENTIRE media notification, so nothing
posts to the tray or the watch (emulator tolerated it). Not a
permission / PathParser / FGS issue — POST_NOTIFICATIONS was verified
granted. Pre-#57 there was no CustomAction, matching the regression.

Remove the custom favorite control; the notification is rebuilt with
only the standard transport controls (audio_service ships their icons).
customAction handler / refreshFavoriteControl left as harmless no-ops
to minimise churn. Like/favorite remains in-app + lock screen.

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

flutter_client/lib/player/audio_handler.dart

@@ -724,31 +724,18 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
   // 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);
+    // No custom favorite MediaControl here. audio_service builds a
+    // PlaybackStateCompat.CustomAction for it and throws
+    // "You must specify an icon resource id to build a CustomAction"
+    // on real builds (the androidIcon doesn't resolve to a usable id),
+    // and that exception aborts the ENTIRE media notification — no
+    // tray or Wear controls at all. Removed; like/favorite remains
+    // available in-app and via the standard lock-screen surface.
     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