feat(app): 完善播放协议搜索与空状态

lib/pages/player/widgets/seek_progress_bar.dart

@@ -13,6 +13,8 @@ import 'loading_progress_track.dart';
 import 'scrub_preview_card.dart';
 
 const Key _inactiveTrackKey = Key('progress-inactive');
+const double _compactTrackSlot = 20;
+const double _trackSlot = 44;
 
 /// Keeps seeks within the playable range so dragging to the edge does not
 /// trigger the player's completion callback before playback resumes.
@@ -241,11 +243,7 @@ class _SeekProgressBarState extends State<SeekProgressBar> {
         widget.thumbnailService != null &&
         (widget.episodeId?.isNotEmpty ?? false);
     final trackHeight = scrubbing ? 6.0 : 2.0;
-    final trackAreaHeight = loading
-        ? (widget.compact ? 20.0 : 44.0)
-        : widget.compact
-        ? (scrubbing ? 32.0 : 20.0)
-        : (scrubbing ? 48.0 : 44.0);
+    final trackAreaHeight = widget.compact ? _compactTrackSlot : _trackSlot;
 
     return LayoutBuilder(
       builder: (context, constraints) {