fix(player): 隔离播放资源所有权并修复黑屏

lib/pages/player/widgets/player_render_stack.dart

@@ -52,10 +52,12 @@ class PlayerRenderStack extends StatefulWidget {
     super.key,
     required this.pageController,
     required this.slots,
+    this.onCurrentVideoVisible,
   });
 
   final PageController pageController;
   final Map<PlayerRenderSlotRole, PlayerRenderSlotData> slots;
+  final VoidCallback? onCurrentVideoVisible;
 
   @override
   State<PlayerRenderStack> createState() => _PlayerRenderStackState();
@@ -68,7 +70,10 @@ class _PlayerRenderStackState extends State<PlayerRenderStack> {
   void initState() {
     super.initState();
     _lastCurrentIndex = _currentSlot.index;
-    _log('init current=${_lastCurrentIndex ?? '-'}');
+    _log(
+      'init current=${_lastCurrentIndex ?? '-'} '
+      'pageController=${identityHashCode(widget.pageController)}',
+    );
   }
 
   @override
@@ -86,7 +91,10 @@ class _PlayerRenderStackState extends State<PlayerRenderStack> {
 
   @override
   void dispose() {
-    _log('dispose current=${_lastCurrentIndex ?? '-'}');
+    _log(
+      'dispose current=${_lastCurrentIndex ?? '-'} '
+      'pageController=${identityHashCode(widget.pageController)}',
+    );
     super.dispose();
   }
 
@@ -189,6 +197,9 @@ class _PlayerRenderStackState extends State<PlayerRenderStack> {
           fallback: slot.fallback,
           warmSlotReused: slot.warmSlotReused,
           waitForPlaybackFrame: slot.waitForPlaybackFrame,
+          onVideoVisible: slot.role == PlayerRenderSlotRole.current
+              ? widget.onCurrentVideoVisible
+              : null,
         ),
       ),
     );

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'