fix(server/m7-379): enricher leaves cover_art_source NULL when MBID missing

internal/coverart/enricher.go

@@ -63,11 +63,15 @@ func (e *Enricher) EnrichAlbum(ctx context.Context, albumID pgtype.UUID) error {
 	}
 
 	// Step 2: MBCAA fallback. Requires fetcher + toggle on + MBID.
+	// When the toggle is disabled OR the album has no MBID, leave
+	// cover_art_source NULL so a future scan can retry once the
+	// scanner heals the MBID. 'none' is reserved for genuine MBCAA
+	// 404s where we know the album really isn't in the archive.
 	if !e.mbcaaOn || e.fetcher == nil {
-		return e.recordCover(ctx, albumID, "", "none")
+		return nil
 	}
 	if row.Mbid == nil || *row.Mbid == "" {
-		return e.recordCover(ctx, albumID, "", "none")
+		return nil
 	}
 
 	body, err := e.fetcher.Fetch(ctx, *row.Mbid)