fix: properly clear cart after order placement

- Use clearCart() from store instead of iterating removeItem()
- Iteration could fail as items are removed during loop
- clearCart() resets cart to initial state atomically

customer-spa/src/pages/Checkout/index.tsx

@@ -237,10 +237,8 @@ export default function Checkout() {
       const data = (response as any).data || response;
 
       if (data.ok && data.order_id) {
-        // Clear cart
-        cart.items.forEach(item => {
-          useCartStore.getState().removeItem(item.key);
-        });
+        // Clear cart - use store method directly
+        useCartStore.getState().clearCart();
 
         toast.success('Order placed successfully!');
         navigate(`/order-received/${data.order_id}?key=${data.order_key}`);