fix: update transport button state when seeking auto-starts playback

Fixed issue where Play/Pause buttons didn't update after clicking on
waveform or timeline slider.

Problem:
- seek() in useAudioPlayer hook only updated currentTime
- But player.seek() now auto-starts playback
- React state (isPlaying, isPaused) wasn't updated
- Transport buttons showed wrong state (Play instead of Pause)

Solution:
- Update isPlaying = true and isPaused = false in seek callback
- Now transport buttons correctly show Pause icon when seeking
- UI state matches actual playback state

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/hooks/useAudioPlayer.ts

@@ -164,6 +164,9 @@ export function useAudioPlayer(): UseAudioPlayerReturn {
 
       await player.seek(time);
       setCurrentTime(time);
+      // Seek now auto-starts playback, so update state accordingly
+      setIsPlaying(true);
+      setIsPaused(false);
     },
     [player]
   );