fix(orders): keep the customer a new order is created for

CreateOrderContractToModel never copied customer_id, so every order from
POST /orders was saved without a customer. Paying it then earned no
EnakPoint or EnakCoin (skipped as NO_CUSTOMER, which is not logged).

The customer must now belong to the order's organization, as
SetOrderCustomer already requires: it is who earns once the order is paid,
and orders.customer_id has no foreign key. A nil UUID means no customer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/processor/order_processor.go

@@ -316,6 +316,18 @@ func resolveLineQuantity(product *entities.Product, quantity int, weight *float6
 }
 
 func (p *OrderProcessorImpl) CreateOrder(ctx context.Context, req *models.CreateOrderRequest, organizationID uuid.UUID) (*models.OrderResponse, error) {
+	// The order's customer earns EnakPoint and EnakCoin once it is paid, so it must be
+	// one of the organization's own; orders.customer_id has no foreign key to catch it.
+	customerID := req.CustomerID
+	if customerID != nil && *customerID == uuid.Nil {
+		customerID = nil
+	}
+	if customerID != nil {
+		if _, err := p.customerRepo.GetByIDAndOrganization(ctx, *customerID, organizationID); err != nil {
+			return nil, fmt.Errorf("customer not found or does not belong to the organization: %w", err)
+		}
+	}
+
 	orderNumber, err := p.orderRepo.GetNextOrderNumber(ctx, organizationID, req.OutletID)
 	if err != nil {
 		return nil, fmt.Errorf("failed to generate order number: %w", err)
@@ -401,7 +413,7 @@ func (p *OrderProcessorImpl) CreateOrder(ctx context.Context, req *models.Create
 		OrganizationID:  organizationID,
 		OutletID:        req.OutletID,
 		UserID:          req.UserID,
-		CustomerID:      req.CustomerID,
+		CustomerID:      customerID,
 		OrderNumber:     orderNumber,
 		TableNumber:     req.TableNumber,
 		OrderType:       entities.OrderType(req.OrderType),