fix: proper seeking behavior with optional auto-play

Complete rewrite of seeking logic to support both scrubbing and
click-to-play functionality with proper state management.

Changes:
1. Added autoPlay parameter to seek() methods across the stack
2. Waveform behavior:
   - Click and drag → scrubs WITHOUT auto-play during drag
   - Mouse up after drag → auto-plays from release position
   - This allows smooth scrubbing while dragging
3. Timeline slider behavior:
   - onChange → seeks WITHOUT auto-play (smooth dragging)
   - onMouseUp/onTouchEnd → auto-plays from final position
4. Transport button state now correctly syncs with playback state

Technical implementation:
- player.seek(time, autoPlay) - autoPlay defaults to false
- If autoPlay=true OR was already playing → continues playback
- If autoPlay=false AND wasn't playing → just seeks (isPaused=true)
- useAudioPlayer.seek() now reads actual player state after seeking

User experience:
✓ Click on waveform → music plays from that position
✓ Drag on waveform → scrubs smoothly, plays on release
✓ Drag timeline slider → scrubs smoothly, plays on release
✓ Transport buttons show correct state (Play/Pause)

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

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

lib/hooks/useAudioPlayer.ts

@@ -14,7 +14,7 @@ export interface UseAudioPlayerReturn {
   play: () => Promise<void>;
   pause: () => void;
   stop: () => void;
-  seek: (time: number) => Promise<void>;
+  seek: (time: number, autoPlay?: boolean) => Promise<void>;
 
   // Volume control
   setVolume: (volume: number) => void;
@@ -159,14 +159,16 @@ export function useAudioPlayer(): UseAudioPlayerReturn {
   }, [player]);
 
   const seek = React.useCallback(
-    async (time: number) => {
+    async (time: number, autoPlay: boolean = false) => {
       if (!player) return;
 
-      await player.seek(time);
+      await player.seek(time, autoPlay);
       setCurrentTime(time);
-      // Seek now auto-starts playback, so update state accordingly
-      setIsPlaying(true);
-      setIsPaused(false);
+
+      // Update state based on what actually happened
+      const state = player.getState();
+      setIsPlaying(state.isPlaying);
+      setIsPaused(state.isPaused);
     },
     [player]
   );