Spotify's playlist embed uses {title, subtitle, audioPreview} per track
instead of {name, artists, album}. Fixes:
- _spTrackItem: reads title as trackName, subtitle as artistName fallback,
audioPreview.url as previewUrl, isExplicit as boolean
- Route: reads entity.authors[0].name for playlist owner, entity.subtitle
for track artist fallback, entity.title fallback for entity.name
- Playlist tracks get playlist cover art as default artwork (no per-track art)
- Removes temporary debug logging
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>