fix(player): 完善进度预览清屏与下拉刷新

lib/pages/player/widgets/scrub_preview_card.dart

@@ -11,8 +11,9 @@ import '../../../core/data/services/sprite_thumbnail_axis.dart';
 import '../../../core/theme/app_colors.dart';
 import '../../../core/widgets/remote_image.dart';
 
-const double scrubPreviewWidth = 120;
+const double scrubPreviewWidth = 96;
 const double scrubPreviewSafeMargin = 12;
+const double _portraitFrameAspect = 9 / 16;
 
 /// 把预览卡片限制在进度条可用宽度内。
 double scrubPreviewLeft({
@@ -64,6 +65,7 @@ class _ScrubPreviewCardState extends State<ScrubPreviewCard> {
   void initState() {
     super.initState();
     widget.spriteAxisService?.addListener(_handleSpriteAxisChanged);
+    _prepareSprite();
     _syncFallbackSource();
   }
 
@@ -74,6 +76,10 @@ class _ScrubPreviewCardState extends State<ScrubPreviewCard> {
       oldWidget.spriteAxisService?.removeListener(_handleSpriteAxisChanged);
       widget.spriteAxisService?.addListener(_handleSpriteAxisChanged);
     }
+    if (oldWidget.thumbnailsUrl != widget.thumbnailsUrl ||
+        oldWidget.position != widget.position) {
+      _prepareSprite();
+    }
     if (oldWidget.service != widget.service ||
         oldWidget.episodeId != widget.episodeId ||
         oldWidget.thumbnailsUrl != widget.thumbnailsUrl) {
@@ -97,6 +103,12 @@ class _ScrubPreviewCardState extends State<ScrubPreviewCard> {
     super.dispose();
   }
 
+  void _prepareSprite() {
+    final service = widget.spriteAxisService;
+    if (service == null) return;
+    unawaited(service.prepareAt(widget.thumbnailsUrl, widget.position));
+  }
+
   void _handleSpriteAxisChanged() {
     if (!mounted) return;
     if (_spriteFrame != null) {
@@ -190,7 +202,8 @@ class _ScrubPreviewCardState extends State<ScrubPreviewCard> {
               ),
             ),
             AspectRatio(
-              aspectRatio: 16 / 9,
+              key: const Key('scrub-preview-frame-box'),
+              aspectRatio: _frameAspect(spriteFrame),
               child: Stack(
                 fit: StackFit.expand,
                 children: [
@@ -229,6 +242,14 @@ class _ScrubPreviewCardState extends State<ScrubPreviewCard> {
   }
 }
 
+double _frameAspect(SpriteThumbnailFrame? frame) {
+  final rect = frame?.sourceRect;
+  if (rect == null || rect.width <= 0 || rect.height <= 0) {
+    return _portraitFrameAspect;
+  }
+  return rect.width / rect.height;
+}
+
 /// 对已解码 sprite 做 sourceRect 裁剪，不触发再次解码。
 class SpriteCropPreview extends StatelessWidget {
   const SpriteCropPreview({