fix(orders): block cancelling an order once the kitchen has started it

Anti-fraud / integrity: a cashier could fire an order to the kitchen, take cash
without recording a payment, then cancel (soft-delete) the unpaid order to erase
it. CancelOrderAsync now only allows cancelling a still-Pending order; once the
kitchen has acted on it (Confirmed/Preparing/Ready) it returns ORDER_IN_PREPARATION
and a started order can no longer be removed — it must be completed (and refunded
through the audited refund flow if needed). Delivered → ORDER_NOT_OPEN; paid →
ORDER_HAS_PAYMENTS (unchanged). Orders are never hard-deleted and every cancel is
already audited with the actor. Applies to all roles, independent of permissions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Meezi.API/Services/OrderService.cs

@@ -995,9 +995,18 @@ public class OrderService : IOrderService
         if (order.Status == OrderStatus.Cancelled)
             return new OrderServiceResult<OrderDto>(false, null, "ORDER_ALREADY_CANCELLED");
 
-        if (!OpenForPaymentStatuses.Contains(order.Status))
+        if (order.Status == OrderStatus.Delivered)
             return new OrderServiceResult<OrderDto>(false, null, "ORDER_NOT_OPEN");
 
+        // Integrity / anti-fraud: once the kitchen has acted on the order
+        // (Confirmed / Preparing / Ready) the food has been produced, so the order
+        // can no longer be cancelled/deleted — otherwise a cashier could fire an
+        // order, take cash without recording a payment, then erase it. Only a
+        // not-yet-started (Pending) order may be cancelled; a started one must be
+        // completed (and refunded via the audited refund flow if needed).
+        if (order.Status != OrderStatus.Pending)
+            return new OrderServiceResult<OrderDto>(false, null, "ORDER_IN_PREPARATION");
+
         // A paid order must be refunded through the payment flow first — cancelling it
         // here would silently strip the recorded money. Block and surface the reason.
         if (order.Payments.Any(p => p.DeletedAt == null))