fix(player): 隔离播放资源所有权并修复黑屏

lib/pages/player/widgets/player_video_surface.dart

@@ -28,6 +28,7 @@ class PlayerVideoSurface extends StatefulWidget {
     this.debugSlot = 'default',
     this.debugIndex,
     this.showFallbackBackground = true,
+    this.onVideoVisible,
   });
 
   final VideoPlayerController? controller;
@@ -57,6 +58,7 @@ class PlayerVideoSurface extends StatefulWidget {
   final bool showFallbackBackground;
   final String videoUrl;
   final bool theater;
+  final VoidCallback? onVideoVisible;
 
   @override
   State<PlayerVideoSurface> createState() => _PlayerVideoSurfaceState();
@@ -73,6 +75,7 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
   bool _confirmationScheduled = false;
   bool _transitioning = false;
   bool _videoVisible = false;
+  bool _videoVisibleNotified = false;
   String? _lastLayerState;
 
   @override
@@ -279,6 +282,7 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
         });
       }
       _logLayer('video', widget.controller?.value);
+      _notifyVideoVisible();
       return;
     }
     if (initial) {
@@ -303,6 +307,7 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
       _placeholderSnapshot = null;
     });
     _logLayer('fade-end', widget.controller?.value);
+    _notifyVideoVisible();
   }
 
   void _resetForControllerChange() {
@@ -314,9 +319,20 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface>
     _confirmationScheduled = false;
     _transitioning = false;
     _videoVisible = false;
+    _videoVisibleNotified = false;
     _lastLayerState = null;
   }
 
+  void _notifyVideoVisible() {
+    if (_videoVisibleNotified) return;
+    _videoVisibleNotified = true;
+    final callback = widget.onVideoVisible;
+    if (callback == null) return;
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (mounted) callback();
+    });
+  }
+
   void _logLayer(String phase, VideoPlayerValue? value) {
     if (!kDebugMode) return;
     final fallback = phase == 'video' || phase == 'fade-end'