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_test.go

@@ -2,6 +2,7 @@ package database
 
 import (
 	"database/sql"
+	"errors"
 	"testing"
 )
 
@@ -58,7 +59,8 @@ func TestGetExternalRelease_Found(t *testing.T) {
 	}
 }
 
-// TestGetExternalRelease_NotFound verifies that a missing release returns sql.ErrNoRows.
+// TestGetExternalRelease_NotFound verifies that a missing release returns an error
+// that wraps sql.ErrNoRows.
 func TestGetExternalRelease_NotFound(t *testing.T) {
 	db, err := New(":memory:")
 	if err != nil {
@@ -67,8 +69,8 @@ func TestGetExternalRelease_NotFound(t *testing.T) {
 	defer db.Close()
 
 	_, err = GetExternalRelease(db, "nonexistent")
-	if err != sql.ErrNoRows {
-		t.Errorf("expected sql.ErrNoRows, got %v", err)
+	if !errors.Is(err, sql.ErrNoRows) {
+		t.Errorf("expected error wrapping sql.ErrNoRows, got %v", err)
 	}
 }