Ensure stable identity for pricing tiers in forms

Adds a tempId to new pricing tiers for stable mapping before backend _id assignment. Updates mapping logic in pricing-tiers form to use tempId or _id for reliable event handling and rendering.

components/modals/product-modal.tsx

@@ -98,7 +98,19 @@ export const ProductModal: React.FC<ProductModalProps> = ({
   const handleAddTier = () => {
     setProductData((prev) => ({
       ...prev,
-      pricing: [...prev.pricing, { minQuantity: 0, pricePerUnit: 0 }],
+      pricing: [
+        ...prev.pricing,
+        {
+          minQuantity: 0,
+          pricePerUnit: 0,
+          // tempId ensures stable identity before backend assigns _id
+          // Using crypto.randomUUID if available, otherwise a timestamp fallback
+          tempId:
+            (typeof crypto !== "undefined" && (crypto as any).randomUUID
+              ? (crypto as any).randomUUID()
+              : `${Date.now()}-${Math.random()}`),
+        },
+      ],
     }));
   };