feat(dashboard): add multi-project allocation UI in AcceptModal and merge on reopen in EditModal

- Add allocations field to LineItem and propagate in api.quotes.update
- Implement allocation cards in AcceptModal Section 3 with per-row project select and sum validation
- Disable previously selected projects within the same item to prevent duplicates
- Merge split items client-side in EditModal when transitioning status to offered

frontend/src/pages/Dashboard/EditModal.tsx

@@ -384,7 +384,26 @@ export function EditModal({ quoteId, onClose }: EditModalProps) {
         li.accepted_ts_id = null;
         li.target_project = null;
         li.target_project_id = null;
+        li.allocations = undefined;
       });
+
+      // ادغام سطرهای تفکیک‌شده حاصل از تخصیص چندپروژه‌ای (الزام ۲)
+      const mergedMap = new Map<string, LineItem>();
+      for (const li of next.line_items) {
+        const key = `${li.material_id}__${li.unit || ""}__${li.unit_price ?? ""}`;
+        const existing = mergedMap.get(key);
+        if (existing) {
+          const q1 = Number(existing.quantity ?? 0);
+          const q2 = Number(li.quantity ?? 0);
+          existing.quantity = Math.round((q1 + q2) * 10000) / 10000;
+          if (existing.unit_price != null && existing.quantity != null) {
+            existing.total_price = existing.unit_price * existing.quantity;
+          }
+        } else {
+          mergedMap.set(key, { ...li });
+        }
+      }
+      next.line_items = Array.from(mergedMap.values());
     } else if (next.status === "accepted") {
       next.arrived_date = null;
       next.line_items.forEach((li) => {