revert(player): MediaSession surface back to 5 advertised actions

Pixel Watch 2 stopped showing controls entirely after v2026.05.13.3's
MediaSession expansion. Reverting the additive pieces:

* systemActions back to the original 5 (play / pause / skipPrev /
  skipNext / seek). stop, skipToQueueItem, setShuffleMode,
  setRepeatMode, setRating removed.
* controls list back to skipPrev / play|pause / skipNext (no stop).
* stop() override removed — let BaseAudioHandler default apply
  (probably needs to be a no-op for the MediaSession to stay alive
  through certain lifecycle events that audio_service triggers
  internally; the override was actually halting the session).
* MediaItem.rating no longer set in _toMediaItem. The Android
  MediaSession.setRating() path requires setRatingType(RATING_HEART)
  to actually expose to controllers, and audio_service doesn't
  surface that config knob — broadcasting an unanchored rating
  appears to make Wear OS reject the session entirely.

Kept in place:
* skipToQueueItem override — still needed for QueueScreen's direct
  handler call (not routed through MediaSession actions).
* setRating override + LikeBridge wiring — harmless if never
  invoked, and lights up automatically if we figure out how to
  configure the rating type later.
* AlbumCoverCache.peekCached for sync artUri seed — that part
  worked, and the failure mode would be a missing cover, not a
  rejected session.

Watch should come back to its previous "sometimes works" state from
v2026.05.13.2 (basic controls only). Getting past that needs proper
MediaSession config that audio_service either doesn't expose or
requires platform-channel work.

flutter_client/lib/player/audio_handler.dart

@@ -315,11 +315,14 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
     final coverPath = (t.albumId.isNotEmpty && _coverCache != null)
         ? _coverCache!.peekCached(t.albumId)
         : null;
-    // MediaItem.rating reflects the user's like state on this track
-    // so external surfaces (Wear's heart button, lock-screen
-    // favorites) render the right filled/outlined icon. Updated on
-    // every track change via _likeBridge.isTrackLiked.
-    final liked = _likeBridge?.isTrackLiked(t.id) ?? false;
+    // MediaItem.rating intentionally NOT set: audio_service propagates
+    // it to MediaSession.setRating(), but the Android session also
+    // needs setRatingType(RATING_HEART) configured to expose that to
+    // controllers — audio_service doesn't surface that config knob,
+    // and broadcasting an unanchored rating made Wear OS reject the
+    // session entirely. The LikeBridge wiring stays in place so
+    // setRating can still fire from any surface that DOES route it,
+    // we just don't advertise it.
     return MediaItem(
       id: t.id,
       title: t.title,
@@ -327,7 +330,6 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
       album: t.albumTitle,
       duration: Duration(seconds: t.durationSec),
       artUri: coverPath != null ? Uri.file(coverPath) : null,
-      rating: Rating.newHeartRating(liked),
       extras: extras.isEmpty ? null : extras,
     );
   }
@@ -412,19 +414,6 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
   @override
   Future<void> skipToPrevious() => _player.seekToPrevious();
 
-  /// Stops playback and dismisses the system notification. BaseAudio
-  /// Handler's default just sets the processing state to idle without
-  /// touching the player, so the just_audio engine kept its audio
-  /// session and external surfaces (Wear, Auto, BT) saw a "paused
-  /// forever" rather than a clean stop. Halting the player releases
-  /// the session and lets super.stop() tear down the foreground
-  /// notification.
-  @override
-  Future<void> stop() async {
-    await _player.stop();
-    await super.stop();
-  }
-
   /// Heart rating from external surfaces (Wear's favorite button,
   /// lock-screen like) → LikesController.toggle(track). We only
   /// route through the bridge when the rating actually flips relative
@@ -498,33 +487,32 @@ class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandl
         MediaControl.skipToPrevious,
         if (playing) MediaControl.pause else MediaControl.play,
         MediaControl.skipToNext,
-        MediaControl.stop,
       ],
       // androidCompactActionIndices tells the system which controls
       // appear in the collapsed/lock-screen view. Without this, some
       // Android versions render the player without working buttons.
-      // Keep this at 3 actions (prev/play-pause/next) — stop lives
-      // in the expanded view only.
       androidCompactActionIndices: const [0, 1, 2],
       // systemActions enumerates which actions the system can invoke
-      // on us. Anything not listed here doesn't route back to the
-      // handler from external surfaces (Wear, Auto, Bluetooth, lock
-      // screen) — Android 13+ silently drops those events. Keep this
-      // in sync with the override methods so each implemented action
-      // is actually advertised.
+      // on us — without play/pause/skip in here, taps on lock-screen
+      // controls don't route back to the handler on Android 13+.
+      //
+      // v2026.05.13.3 added stop, skipToQueueItem, setShuffleMode,
+      // setRepeatMode, and setRating to this set; reverted because
+      // Pixel Watch 2 stopped showing controls entirely after that
+      // change. The MediaSession contract on Wear OS requires more
+      // setup than just advertising the action (e.g. setRatingType
+      // for setRating) and audio_service doesn't expose those knobs.
+      // Keep the override methods themselves (skipToQueueItem is
+      // still routed via QueueScreen's direct handler call;
+      // setRating is harmless if never invoked) so we don't lose
+      // the underlying functionality — just don't tell the system
+      // we support them.
       systemActions: const {
         MediaAction.play,
         MediaAction.pause,
-        MediaAction.stop,
         MediaAction.skipToNext,
         MediaAction.skipToPrevious,
-        MediaAction.skipToQueueItem,
         MediaAction.seek,
-        MediaAction.setShuffleMode,
-        MediaAction.setRepeatMode,
-        // Heart rating — Wear and lock screen render this as a like
-        // button. Routed to LikesController via _likeBridge.
-        MediaAction.setRating,
       },
       processingState: switch (_player.processingState) {
         ProcessingState.idle => AudioProcessingState.idle,