feat(player): 保持屏幕常亮并自动恢复播放

lib/core/data/services/playback_session.dart

@@ -92,6 +92,7 @@ class PlaybackSession extends ChangeNotifier {
     }
     return slot.player;
   }
+
   bool get loading => _loading;
   bool get userWantsPlay => _userWantsPlay;
   bool get canAutoAdvance => _mayPlay && !_loading && active != null;
@@ -103,6 +104,10 @@ class PlaybackSession extends ChangeNotifier {
   Future<void> get playbackSettled => _operations;
   Future<void> get preloadSettled => _preloadTask;
 
+  /// 当前页面可见、无浮层遮挡且存在可用播放器时可安全恢复。
+  bool get canResumeAfterBackground =>
+      !_closed && _routeVisible && !_overlayOpen && active != null;
+
   bool get _visible => !_closed && _appResumed && _routeVisible;
   bool get _mayPlay => _visible && !_overlayOpen && _userWantsPlay;