425f12db38
Changes the AlbumCoverProvider and ArtistArtProvider interfaces from MBID-only string parameters to ref-struct signatures so name-based providers (Deezer, Last.fm in upcoming tasks) can act on rows without MBIDs. Today, 53 of 213 artists in the dev DB have NULL MBIDs — featured artists, remixers, and compilation contributors created from track-tag splits where the primary-artist MBID is in the file but collaborator IDs aren't. These rows are unreachable by the current MBID-only chain. Refactoring the interface unblocks future name-based providers from acting on them. TheAudioDB and MBCAA keep MBID-only behavior internally: they return ErrNotFound when ref.MBID is empty rather than attempting a name-based fallback. The MBID guard inside EnrichAlbum/EnrichArtist is removed; providers receive the ref unconditionally and decide whether they can act on it. GetAlbumWithFirstTrackPath now JOINs artists to return artist_name alongside the existing fields, supporting AlbumRef construction. No behavioral change today (only TheAudioDB + MBCAA registered, both keep MBID-only behavior). The change unblocks T3 (Deezer) and T4 (Last.fm) which can now register and act on every artist/album regardless of MBID presence. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>