fix(delivery): accept root@% credential for CloudDM registration

PR #128 looks up the root credential with account_host = 'localhost',
which never matches under the single root@% account model. Widen the
lookup to account_host IN ('%', 'localhost'), consistent with the
compatibility strategy in deploymentCredentialVars.

server/internal/service/delivery.go

@@ -2046,7 +2046,7 @@ func (s *DeliveryService) RegisterCloudDM(ctx context.Context, taskID string) er
 	}
 	var credential model.DeploymentCredential
 	if err := s.db.WithContext(ctx).
-		Where("task_id = ? AND username = ? AND account_host = ? AND status IN ?", taskID, "root", "localhost", []string{"pending", "available"}).
+		Where("task_id = ? AND username = ? AND account_host IN ? AND status IN ?", taskID, "root", []string{"%", "localhost"}, []string{"pending", "available"}).
 		First(&credential).Error; err != nil {
 		return fmt.Errorf("CloudDM registration requires the MySQL root credential: %w", err)
 	}