fix: remove undefined audioSource reference in AudioPlayer

- Removed audioSource.duration fallback since component only receives audioUrl
- Duration is tracked internally in AudioPlayer state via onLoadedMetadata

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

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

Author: aramb-dev

src/components/transcription/TranscriptionStudio.tsx

@@ -201,7 +201,7 @@ const AudioPlayer: React.FC<AudioPlayerProps> = ({
               <div className="space-y-1">
                 <div className="flex justify-between text-xs text-gray-500">
                   <span>{formatDuration(currentTime)}</span>
-                  <span>{formatDuration(duration || audioSource.duration)}</span>
+                  <span>{formatDuration(duration)}</span>
                 </div>
                 <div
                   className="h-1 cursor-pointer overflow-hidden rounded-full bg-gray-200 transition-all duration-100 hover:h-2"