Adds Deezer as a name-based provider in the artist + album chains.
Public read API, no API key required, default-on. Rate-limited to
5 req/s (well under their 50/5s per-IP ceiling).
Includes exact-name match guard against false positives: if the top
search result's artist/album name doesn't case-insensitive-match
what we sent, returns ErrNotFound rather than persisting the wrong
art. This is critical for one-word artist names (e.g. "Time")
where Deezer's relevance ranking can't distinguish.
Provides the long-promised path for the 53 MBID-less artist rows in
the dev DB (featured/collab artists from track-tag splits) which
TheAudioDB cannot reach.
For artists, Deezer returns a single image which we use as thumb;
fanart stays nil. The enricher's persistence layer already handles
thumb-only correctly.
bvandeusen