fix(player): 完善进度预览清屏与下拉刷新

lib/pages/player/widgets/seek_progress_bar.dart

@@ -170,11 +170,28 @@ class _SeekProgressBarState extends State<SeekProgressBar> {
     setState(() => _buffering = buffering);
   }
 
+  void _endPointerDrag() {
+    if (!_dragging) {
+      _pointerMoved = false;
+      _pointerStart = null;
+      _dragStartFraction = null;
+      return;
+    }
+    final duration = widget.valueListenable?.value.duration ?? Duration.zero;
+    final fraction = _previewFraction.value ?? _dragStartFraction ?? 0;
+    unawaited(_finish(fraction, duration));
+  }
+
   Future<void> _finish(double fraction, Duration duration) async {
     final startedAt = _dragStartFraction;
     _dragStartFraction = null;
     if (widget.locked || !_dragging || startedAt == null) return;
-    setState(() => _dragging = false);
+    _dragging = false;
+    if (!mounted) {
+      widget.onScrubEnd?.call();
+      return;
+    }
+    setState(() {});
     _pointerMoved = false;
     _pointerStart = null;
     widget.thumbnailService?.cancelPending();
@@ -287,20 +304,8 @@ class _SeekProgressBarState extends State<SeekProgressBar> {
                               _pointerMoved = true;
                             }
                           },
-                          onPointerUp: (_) {
-                            if (!_dragging) {
-                              _pointerMoved = false;
-                              _pointerStart = null;
-                              _dragStartFraction = null;
-                            }
-                          },
-                          onPointerCancel: (_) {
-                            if (!_dragging) {
-                              _pointerMoved = false;
-                              _pointerStart = null;
-                              _dragStartFraction = null;
-                            }
-                          },
+                          onPointerUp: (_) => _endPointerDrag(),
+                          onPointerCancel: (_) => _endPointerDrag(),
                           child: Slider(
                             value: fraction,
                             // 轨道与上方文案共用同一层水平内边距，避免 Slider 默认内缩。