fix: address code review findings

internal/database/external_releases.go

@@ -169,6 +169,12 @@ func SetReleaseIgnored(db *DB, rgid string, ignored bool) error {
 // GetExternalReleasesByArtistWithCache returns cached external_release rows for a given artist_id
 // that are within the specified TTL.
 func GetExternalReleasesByArtistWithCache(db *DB, artistID string, ttl time.Duration) ([]ExternalRelease, error) {
+	// A zero or negative TTL means "no cache" — always expire. Returning early
+	// here avoids the boundary pitfall where cutoff == now would treat rows
+	// cached in the current second as fresh.
+	if ttl <= 0 {
+		return nil, nil
+	}
 	// cached_at is stored in the "2006-01-02 15:04:05" UTC layout via
 	// FormatCachedAt. Compare against an explicitly formatted cutoff string in
 	// the same layout so the lexicographic comparison is a valid time ordering.