feat(embed): YouTube playlist/album as audio on the site
An audio-only YouTube embed with ?list=… now renders as an album card (same
style as own albums): cover + album name + numbered track list (titles via the
oEmbed proxy; video IDs via getPlaylist). Clicking a track or the album art
plays via the site audio player (loadPlaylist on index → next/prev within the
album; title/cover update per track; row highlight via #track-<videoId>).
Duration per track is empty (—:—) — not available without a YouTube Data API key.
busters audio-player.js?v=23, embed-player.js?v=12, embed.css?v=7.
Co-Authored-By: Claude <noreply@…>