refactor: 重構 VendorProduct API 與新增進貨單重複檢查前端邏輯

1. 將 VendorProductController 中的 Eloquent 關聯操作改為透過 ProcurementService 使用 DB 操作，解除跨模組 Model 直接依賴。
2. ProcurementService 加入 vendor product 的資料存取方法。
3. 進貨單建立前端 (GoodsReceipt/Create.tsx) 新增重複進貨檢查與警告對話框邏輯。

app/Modules/Procurement/Services/ProcurementService.php

@@ -99,4 +99,52 @@ class ProcurementService implements ProcurementServiceInterface
     {
         return \App\Modules\Procurement\Models\Vendor::whereIn('id', $ids)->get(['id', 'name', 'code']);
     }
+
+    public function attachProductToVendor(int $vendorId, int $productId, ?float $lastPrice): void
+    {
+        \Illuminate\Support\Facades\DB::table('product_vendor')->insert([
+            'vendor_id' => $vendorId,
+            'product_id' => $productId,
+            'last_price' => $lastPrice,
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+    }
+
+    public function updateVendorProductPrice(int $vendorId, int $productId, ?float $lastPrice): void
+    {
+        \Illuminate\Support\Facades\DB::table('product_vendor')
+            ->where('vendor_id', $vendorId)
+            ->where('product_id', $productId)
+            ->update([
+                'last_price' => $lastPrice,
+                'updated_at' => now(),
+            ]);
+    }
+
+    public function checkVendorHasProduct(int $vendorId, int $productId): bool
+    {
+        return \Illuminate\Support\Facades\DB::table('product_vendor')
+            ->where('vendor_id', $vendorId)
+            ->where('product_id', $productId)
+            ->exists();
+    }
+
+    public function getVendorProductPrice(int $vendorId, int $productId): ?float
+    {
+        $pivot = \Illuminate\Support\Facades\DB::table('product_vendor')
+            ->where('vendor_id', $vendorId)
+            ->where('product_id', $productId)
+            ->first();
+
+        return $pivot ? (float) $pivot->last_price : null;
+    }
+
+    public function detachProductFromVendor(int $vendorId, int $productId): void
+    {
+        \Illuminate\Support\Facades\DB::table('product_vendor')
+            ->where('vendor_id', $vendorId)
+            ->where('product_id', $productId)
+            ->delete();
+    }
 }