fix: address fourth code review findings

- Fix FK constraint violation in SyncArtistDiscography: delete
  notifications_sent rows before external_releases to prevent
  constraint failure when re-syncing artists with prior notifications.
- Implement per-artist type filtering: FilterReleaseGroups now accepts
  FilterOptions with IgnoreSingles/IgnoreCompilations flags, read from
  artist_settings table via getArtistFilterOptions.
- Fix inconsistent error wrapping: GetExternalRelease now wraps errors
  with fmt.Errorf like all other functions in the package; updated test
  to use errors.Is for sql.ErrNoRows check.
- Add tests: FilterReleaseGroups ignore singles/compilations,
  SyncArtistDiscography per-artist type filtering, and FK-safe resync.

internal/database/external_releases.go

@@ -9,7 +9,6 @@ import (
 )
 
 // GetExternalRelease retrieves an external_release row by RGID.
-// Returns sql.ErrNoRows if the release is not found.
 func GetExternalRelease(db *DB, rgid string) (*ExternalRelease, error) {
 	var r ExternalRelease
 	var cachedAt sql.NullTime
@@ -18,7 +17,7 @@ func GetExternalRelease(db *DB, rgid string) (*ExternalRelease, error) {
 		rgid,
 	).Scan(&r.RGID, &r.ArtistID, &r.Title, &r.Type, &r.ReleaseDate, &r.IsIgnored, &cachedAt)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("get external release: %w", err)
 	}
 	if cachedAt.Valid {
 		r.CachedAt = cachedAt.Time