The title/artist fallback search took results[0]'s artwork unconditionally, so
a loose full-text match returned the wrong album's cover (the 'new sources give
incorrect art' reports). Now it pulls a few results and only accepts one whose
title matches (subset, to allow Deluxe/Remaster) AND whose artist matches
exactly — the artist being the strong guard against wrong covers. Falls back to
an exact title match when a result carries no artist.
The album's own stored source-id path is unchanged (that id is authoritative).
Tests: wrong-artist rejected, skips wrong result for a matching one, + unit
coverage of the matcher (deluxe/feat/stopwords accepted, wrong artist/title
rejected).
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