When a music.youtube.com/channel/... URL is subscribed, use ytmusicapi
to enumerate the artist's album and single releases instead of yt-dlp
flat-extract, which only returns individual topic video uploads.
Each release is tracked as an OLAK5uy_ playlist ID in seen_ids, so new
albums and singles are detected and queued automatically on each check.
- Add extract_ytmusic_artist_releases() using ytmusicapi.get_artist()
and get_artist_albums() for full pagination
- Route YTMusic URLs in add_subscription() and _check_one_unlocked()
- Add ytmusicapi dependency
- Add 31 tests covering URL detection, extraction, and manager integration
