feat(procurement): 採購單號格式增加 PO 前綴

app/Modules/Procurement/Controllers/PurchaseOrderController.php

@@ -187,9 +187,10 @@ class PurchaseOrderController extends Controller
         try {
             DB::beginTransaction();
 
-            // 生成單號：YYYYMMDD001
+            // 生成單號：POYYYYMMDD001
             $today = now()->format('Ymd');
-            $lastOrder = PurchaseOrder::where('code', 'like', $today . '%')
+            $prefix = 'PO' . $today;
+            $lastOrder = PurchaseOrder::where('code', 'like', $prefix . '%')
                 ->lockForUpdate() // 鎖定以避免並發衝突
                 ->orderBy('code', 'desc')
                 ->first();
@@ -201,7 +202,7 @@ class PurchaseOrderController extends Controller
             } else {
                 $sequence = '001';
             }
-            $code = $today . $sequence;
+            $code = $prefix . $sequence;
 
             $totalAmount = 0;
             foreach ($validated['items'] as $item) {