fix(music): mark only the active sleep timer preset selected

All timed presets shared one 'timed' bool, so arming any of 15/30/60
minutes checkmarked all three. The service now retains the armed
duration (sleepTimerDuration) and the menu marks the matching preset.

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

lib/services/music/music_playback_service.dart

@@ -117,6 +117,10 @@ abstract class MusicPlaybackService extends ChangeNotifier {
   /// inactive.
   DateTime? get sleepTimerEndsAt;
 
+  /// The duration the timed sleep timer was armed with (for marking the
+  /// chosen preset); null in end-of-track mode or when inactive.
+  Duration? get sleepTimerDuration;
+
   /// Whether the sleep timer pauses at the end of the current track instead
   /// of after a fixed duration.
   bool get sleepTimerEndOfTrack;
@@ -233,6 +237,9 @@ class StubMusicPlaybackService extends MusicPlaybackService {
   @override
   DateTime? get sleepTimerEndsAt => null;
 
+  @override
+  Duration? get sleepTimerDuration => null;
+
   @override
   bool get sleepTimerEndOfTrack => false;
 

lib/services/music/music_playback_service_impl.dart

@@ -129,6 +129,7 @@ class MusicPlaybackServiceImpl extends MusicPlaybackService with WidgetsBindingO
 
   Timer? _sleepTimer;
   DateTime? _sleepTimerEndsAt;
+  Duration? _sleepTimerDuration;
   bool _sleepTimerEndOfTrack = false;
 
   final StreamController<Duration> _positionController = StreamController<Duration>.broadcast();
@@ -186,6 +187,9 @@ class MusicPlaybackServiceImpl extends MusicPlaybackService with WidgetsBindingO
   @override
   DateTime? get sleepTimerEndsAt => _sleepTimerEndsAt;
 
+  @override
+  Duration? get sleepTimerDuration => _sleepTimerDuration;
+
   @override
   bool get sleepTimerEndOfTrack => _sleepTimerEndOfTrack;
 
@@ -932,10 +936,12 @@ class MusicPlaybackServiceImpl extends MusicPlaybackService with WidgetsBindingO
     _sleepTimer?.cancel();
     _sleepTimer = null;
     _sleepTimerEndsAt = null;
+    _sleepTimerDuration = null;
     final hadEndOfTrack = _sleepTimerEndOfTrack;
     _sleepTimerEndOfTrack = endOfTrack;
     if (!endOfTrack && duration != null) {
       _sleepTimerEndsAt = DateTime.now().add(duration);
+      _sleepTimerDuration = duration;
       _sleepTimer = Timer(duration, _onSleepTimerFired);
     }
     // End-of-track mode suppresses gapless arming (and leaving it restores
@@ -949,6 +955,7 @@ class MusicPlaybackServiceImpl extends MusicPlaybackService with WidgetsBindingO
   void _onSleepTimerFired() {
     _sleepTimer = null;
     _sleepTimerEndsAt = null;
+    _sleepTimerDuration = null;
     unawaited(pause());
     notifyListeners();
   }
@@ -957,6 +964,7 @@ class MusicPlaybackServiceImpl extends MusicPlaybackService with WidgetsBindingO
     _sleepTimer?.cancel();
     _sleepTimer = null;
     _sleepTimerEndsAt = null;
+    _sleepTimerDuration = null;
     _sleepTimerEndOfTrack = false;
   }