feat(integration): 完善外部 API 對接邏輯與安全性

1. 新增 API Rate Limiting (每分鐘 60 次)
2. 實作 ProductServiceInterface 與 findOrCreateWarehouseByName 解決跨模組耦合問題
3. 強化 OrderSync API 驗證 (price 欄位限制最小 0、payment_method 加上允許白名單)
4. 實作 OrderSync API 冪等性處理，重複訂單直接回傳現有資訊
5. 修正 ProductSync API 同步邏輯，每次同步皆會更新產品分類與單位
6. 完善 integration API 對接手冊內容與 UI 排版

app/Modules/Integration/Controllers/ProductSyncController.php

@@ -4,14 +4,14 @@ namespace App\Modules\Integration\Controllers;
 
 use App\Http\Controllers\Controller;
 use Illuminate\Http\Request;
-use App\Modules\Inventory\Services\ProductService;
+use App\Modules\Inventory\Contracts\ProductServiceInterface;
 use Illuminate\Support\Facades\Log;
 
 class ProductSyncController extends Controller
 {
     protected $productService;
 
-    public function __construct(ProductService $productService)
+    public function __construct(ProductServiceInterface $productService)
     {
         $this->productService = $productService;
     }
@@ -21,7 +21,7 @@ class ProductSyncController extends Controller
         $request->validate([
             'external_pos_id' => 'required|string',
             'name' => 'required|string',
-            'price' => 'nullable|numeric',
+            'price' => 'nullable|numeric|min:0',
             'barcode' => 'nullable|string',
             'category' => 'nullable|string',
             'unit' => 'nullable|string',
@@ -40,7 +40,9 @@ class ProductSyncController extends Controller
             ]);
         } catch (\Exception $e) {
             Log::error('Product Sync Failed', ['error' => $e->getMessage(), 'payload' => $request->all()]);
-            return response()->json(['message' => 'Sync failed'], 500);
+            return response()->json([
+                'message' => 'Sync failed: ' . $e->getMessage(),
+            ], 500);
         }
     }
 }