fix: prevent waveform seekbar flashing back to old position on seek

When clicking/dragging the waveform seekbar, the playback position would
briefly flash back to the previous position before snapping to the new
one.

The seek function optimistically updates the store with the target
position immediately but debounces the actual audio_seek IPC call by
100ms. During that window, audio:progress events from the Rust backend
continue to arrive carrying the old playback position, overwriting the
optimistic update and causing the visual flash.

The fix skips incoming audio:progress events while a seek debounce is
pending, since the store already holds the correct target position. Once
the debounce fires and audio_seek is sent to the backend, progress
events resume normally.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/store/playerStore.ts

@@ -159,6 +159,11 @@ function handleAudioPlaying(_duration: number) {
 }
 
 function handleAudioProgress(current_time: number, duration: number) {
+  // While a seek is pending, the store already holds the optimistic target
+  // position.  Accepting stale progress from the Rust engine would briefly
+  // snap the waveform back to the old position before the seek completes.
+  if (seekDebounce) return;
+
   const store = usePlayerStore.getState();
   const track = store.currentTrack;
   if (!track) return;