Pache711: a cover-art finding showed the (correct) found album art next to a
(wrong) artist image with one "Apply Art" button — no way to take one and
skip the other. Turned out "Apply Art" only ever applied ALBUM art anyway;
the artist image was display-only context, so the bundling was an illusion
the UI created.
Now the finding is genuinely multi-target:
- scan (missing_cover_art.py): also searches for an artist image (always, so
a WRONG existing one can be replaced — Boulder's call), name-matched
exactly. Stored as found_artist_url only when it differs from the current
artist thumb, so nothing is offered when there's nothing to change.
- apply (_fix_missing_cover_art): honors a target via _fix_action —
'album' (default, unchanged "Apply Art" behavior: DB thumb + embed +
cover.jpg), 'artist' (the artist's DB image), or 'both'. New _fix_artist_art
sets artists.thumb_url for the album's artist.
- UI: each found image gets its own apply button — "Use for album" /
"Use for artist". Applying either resolves the finding, so taking the
correct one and ignoring the wrong one IS "fix one, dismiss the other".
Current artist art shows as "(current)" context with no button.
Default stays album-only, so the plain Apply Art button and every existing
caller behave exactly as before. Tests: 5 on the apply targets (artist-only /
album-only / default / both / missing-url) against a real SQLite DB, plus the
existing cover-art suite updated for the new artist search. 107 repair/
cover-art/UI-integrity tests pass.