feat(player): handle stop/skip/speed media-session commands

The platforms advertise stop, skip forward/backward, and playback-rate
commands by default, but both the music and video handlers silently
dropped them (Android Auto/Bluetooth stop and FF/rewind did nothing;
iOS/macOS showed a dead rate control). setControlsEnabled now manages
those controls: music handles Stop and in-track skips and stops
advertising a speed control; video handles Stop (exit, matching the
companion remote), skips via a shared relative-seek helper, and rate
changes through player.setRate. Skip commands stay off on iOS/macOS
where they would displace the next/previous lock-screen buttons.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/services/music/music_playback_service_test.dart

@@ -451,8 +451,19 @@ class FakeMediaControlsManager extends MediaControlsManager {
     bool force = false,
   }) async {}
 
+  final List<({bool canGoNext, bool canStop, bool canSkip, bool canSetSpeed})> controlSyncs = [];
+
   @override
-  Future<void> setControlsEnabled({bool canGoNext = false, bool canGoPrevious = false, bool canSeek = false}) async {}
+  Future<void> setControlsEnabled({
+    bool canGoNext = false,
+    bool canGoPrevious = false,
+    bool canSeek = false,
+    bool canStop = false,
+    bool canSkip = false,
+    bool canSetSpeed = false,
+  }) async {
+    controlSyncs.add((canGoNext: canGoNext, canStop: canStop, canSkip: canSkip, canSetSpeed: canSetSpeed));
+  }
 
   @override
   Future<void> clear() async {
@@ -739,6 +750,46 @@ void main() {
     expect(h.player.playCalls, 1);
   });
 
+  test('OS stop command stops the session', () async {
+    await h.playTracks([t1, t2]);
+    final player = h.player;
+
+    h.controls.eventsCtrl.add(const StopEvent());
+    await pumpEventQueue();
+
+    expect(h.service.status, MusicPlaybackStatus.idle);
+    expect(h.service.currentTrack, isNull);
+    expect(player.disposed, isTrue);
+  });
+
+  test('OS skip commands seek within the track, clamped to its bounds', () async {
+    await h.playTracks([t1, t2]);
+    h.player.setPosition(const Duration(seconds: 30));
+
+    h.controls.eventsCtrl.add(const SkipForwardEvent(Duration(seconds: 15)));
+    await pumpEventQueue();
+    expect(h.player.seeks, [const Duration(seconds: 45)]);
+
+    h.controls.eventsCtrl.add(const SkipBackwardEvent(null)); // default interval
+    await pumpEventQueue();
+    expect(h.player.seeks.last, const Duration(seconds: 30));
+
+    h.player.setPosition(const Duration(seconds: 5));
+    h.controls.eventsCtrl.add(const SkipBackwardEvent(Duration(seconds: 15)));
+    await pumpEventQueue();
+    expect(h.player.seeks.last, Duration.zero);
+  });
+
+  test('music advertises stop and skip but never a speed control', () async {
+    await h.playTracks([t1, t2]);
+
+    expect(h.controls.controlSyncs, isNotEmpty);
+    final last = h.controls.controlSyncs.last;
+    expect(last.canStop, isTrue);
+    expect(last.canSkip, isTrue);
+    expect(last.canSetSpeed, isFalse);
+  });
+
   test('interruption without shouldResume stays paused', () async {
     await h.playTracks([t1]);