JellyfinArtist sets self.thumb (→ artists.thumb_url on scan); JellyfinAlbum
never did. So for Jellyfin/Emby the library scan read getattr(album, 'thumb',
None) == None and albums.thumb_url stayed empty for the WHOLE library. Two
downstream effects: blank album art in the web UI, and the Cover Art Filler
flagging every album as "missing cover art" (db_missing = empty thumb_url) —
making the filler the only thing that ever populated the column, which is
backwards. It should come from the scan, like artist thumbs do.
Fix: JellyfinAlbum.thumb = /Items/<id>/Images/Primary (same shape as the artist
thumb, which already normalizes + displays via fix_artist_image_url). Now the
scan stores album thumbs, the UI shows art, and the filler only flags albums
that are genuinely missing art. Navidrome + Plex already set album thumbs.
Tests: album exposes the Primary-image thumb, None without an id, same shape as
the artist thumb.
