fix(quick-10): add migration 5 and fix entity cache for composite album key

- Migration 5 rebuilds release_groups with UNIQUE(name, album_artist_credit_id)
- Drops and recreates track_metadata VIEW during table rebuild
- Temporarily disables FK checks for safe table rebuild
- Entity cache now keys by album name + artist credit ID
- Update tests to use composite cache keys

backend/library/library.go

@@ -1261,8 +1261,18 @@ func (l *Library) resolveReleaseGroup(
 		return sql.NullInt64{}
 	}
 
+	// Build composite cache key: "albumName\x00artistCreditID"
+	// (or "albumName\x00-1" if no artist).  This prevents albums
+	// with the same name by different artists from colliding.
+	artistID := int64(-1)
+	if albumArtistCreditID.Valid {
+		artistID = albumArtistCreditID.Int64
+	}
+
+	cacheKey := fmt.Sprintf("%s\x00%d", tags.Album, artistID)
+
 	// Check cache first.
-	if cached, ok := cache.releaseGroups[tags.Album]; ok {
+	if cached, ok := cache.releaseGroups[cacheKey]; ok {
 		// If the cached release group lacks cover art and we now
 		// have it, update it.
 		if coverArtID.Valid && !cached.CoverArtID.Valid {
@@ -1280,7 +1290,7 @@ func (l *Library) resolveReleaseGroup(
 				)
 			} else {
 				cached.CoverArtID = coverArtID
-				cache.releaseGroups[tags.Album] = cached
+				cache.releaseGroups[cacheKey] = cached
 			}
 		}
 
@@ -1321,7 +1331,7 @@ func (l *Library) resolveReleaseGroup(
 		}
 	}
 
-	cache.releaseGroups[tags.Album] = rg
+	cache.releaseGroups[cacheKey] = rg
 
 	return sql.NullInt64{Int64: rg.ID, Valid: true}
 }

backend/library/scan_test.go

@@ -533,7 +533,9 @@ func TestResolveReleaseGroup(t *testing.T) {
 	}
 
 	// Cover art should be updated on the cached release group.
-	cachedRG := cache.releaseGroups["A Night at the Opera"]
+	// Cache key is composite: "albumName\x00artistCreditID".
+	cacheKey := fmt.Sprintf("%s\x00%d", "A Night at the Opera", ac.ID)
+	cachedRG := cache.releaseGroups[cacheKey]
 	if !cachedRG.CoverArtID.Valid {
 		t.Error("expected CoverArtID to be set after update")
 	}
@@ -559,7 +561,8 @@ func TestResolveReleaseGroup_CacheHit(t *testing.T) {
 	q := lib.db.Queries
 
 	// Pre-populate cache with a known release group.
-	cache.releaseGroups["Cached Album"] = sqlcgen.ReleaseGroup{
+	// Cache key is composite: "albumName\x00artistCreditID" (use -1 for no artist).
+	cache.releaseGroups[fmt.Sprintf("%s\x00%d", "Cached Album", int64(-1))] = sqlcgen.ReleaseGroup{
 		ID:   42,
 		Name: "Cached Album",
 	}