chore: add custom_services and booking_custom_services to test DB cleanup lists

Add custom_services and booking_custom_services to testdb dropOrder and TruncateTables lists, and add CreateTestCustomService/DeleteCustomService fixture helpers.

Ultraworked with Sisyphus (https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/testutils/fixtures/fixtures.go

@@ -193,6 +193,28 @@ func DeleteBooking(pool *pgxpool.Pool, bookingID string) error {
 	return err
 }
 
+func CreateTestCustomService(pool *pgxpool.Pool) (string, error) {
+	ctx := context.Background()
+	var serviceID string
+	err := pool.QueryRow(ctx, `
+		INSERT INTO custom_services (name, description, price, duration_minutes, minimum_age_required)
+		VALUES ($1, $2, $3, $4, $5)
+		RETURNING id
+	`, "Test Custom Service", "A test custom service", 75.00, 45, 16).Scan(&serviceID)
+
+	if err != nil {
+		return "", fmt.Errorf("failed to create custom service: %w", err)
+	}
+
+	return serviceID, nil
+}
+
+func DeleteCustomService(pool *pgxpool.Pool, serviceID string) error {
+	ctx := context.Background()
+	_, err := pool.Exec(ctx, "DELETE FROM custom_services WHERE id = $1", serviceID)
+	return err
+}
+
 // SafeDeleteUser wraps DeleteUser and returns error (for tests that care about cleanup failure)
 func SafeDeleteUser(db *pgxpool.Pool, userID string) error {
 	return DeleteUser(db, userID)