fix(ci): clean up lint and dead code

backend/internal/repository/migrations_runner.go

@@ -301,7 +301,9 @@ func findDuplicatePaymentOrderOutTradeNos(ctx context.Context, db *sql.DB) ([]st
 	if err != nil {
 		return nil, err
 	}
-	defer rows.Close()
+	defer func() {
+		_ = rows.Close()
+	}()
 
 	duplicates := make([]string, 0, 5)
 	for rows.Next() {

backend/internal/repository/user_repo.go

@@ -739,10 +739,6 @@ func (r *userRepository) ExistsByEmail(ctx context.Context, email string) (bool,
 	return r.client.User.Query().Where(userEmailLookupPredicate(email)).Exist(ctx)
 }
 
-func (r *userRepository) ensureNormalizedEmailAvailable(ctx context.Context, userID int64, email string) error {
-	return ensureNormalizedEmailAvailableWithClient(ctx, clientFromContext(ctx, r.client), userID, email)
-}
-
 func ensureNormalizedEmailAvailableWithClient(ctx context.Context, client *dbent.Client, userID int64, email string) error {
 	client = clientFromContext(ctx, client)
 	if client == nil {

backend/internal/repository/user_repo_email_lookup_unit_test.go

@@ -209,10 +209,10 @@ func TestUserRepositoryCreateSerializesNormalizedEmailConflictsUnderConcurrency(
 	successes := 0
 	conflicts := 0
 	for _, err := range errors {
-		switch {
-		case err == nil:
+		switch err {
+		case nil:
 			successes++
-		case err == service.ErrEmailExists:
+		case service.ErrEmailExists:
 			conflicts++
 		default:
 			t.Fatalf("unexpected create error: %v", err)