Opening a library artist from a non-library search result (e.g. a
MusicBrainz hit) leaves the artist-detail page holding the source ID —
the MBID — not the integer library PK. The standard /api/artist-detail
route resolves that via find_library_artist_for_source, but the
enhanced-view (`/api/library/artist/<id>/enhanced`) and quality-analysis
endpoints call get_artist_full_detail directly with whatever ID the page
holds. Its lookup was `WHERE id = ?` only, so it 404'd ("Artist with ID
<mbid> not found") and the enhanced view failed to load.
When the direct PK lookup misses, fall back to matching any per-service
ID column, reusing SOURCE_ID_FIELD as the single source of truth so the
resolution covers every source (MusicBrainz, Spotify, Deezer, iTunes,
Discogs, Hydrabase, Amazon), not just MusicBrainz.
Adds 4 isolated DB-method tests: direct PK still works, resolves by
MBID, resolves by Spotify ID, and unknown IDs still 404.
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