fix: playback starts from seeked position instead of beginning

Fixed critical bug where playback always started from 0:00 regardless
of seek position or pause state.

Root cause:
- play() method called stop() which reset pauseTime to 0
- Then it checked isPaused (now false) and pauseTime (now 0)
- Result: always played from beginning

Solution:
- Calculate offset BEFORE calling stop()
- Preserve the paused position or start offset
- Then stop and recreate source node with correct offset

Now playback correctly starts from:
- Seeked position (waveform click or timeline slider)
- Paused position (when resuming after pause)
- Specified start offset (when provided)

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

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

lib/audio/player.ts

@@ -40,6 +40,9 @@ export class AudioPlayer {
     // Resume audio context if needed
     await resumeAudioContext();
 
+    // Calculate start offset BEFORE stopping (since stop() resets pauseTime)
+    const offset = this.isPaused ? this.pauseTime : startOffset;
+
     // Stop any existing playback
     this.stop();
 
@@ -48,8 +51,7 @@ export class AudioPlayer {
     this.sourceNode.buffer = this.audioBuffer;
     this.sourceNode.connect(this.gainNode);
 
-    // Calculate start offset
-    const offset = this.isPaused ? this.pauseTime : startOffset;
+    // Set start time
     this.startTime = this.audioContext.currentTime - offset;
 
     // Start playback