新增 POS 庫存查詢 API：實作 InventorySyncController 與相關 Service 邏輯，並更新 API 整合手冊

app/Modules/Inventory/Services/InventoryService.php

@@ -644,4 +644,34 @@ class InventoryService implements InventoryServiceInterface
             ]
         );
     }
+
+    /**
+     * 取得特定倉庫代碼的所屬商品總庫存 (給 POS/外部系統同步使用)
+     *
+     * @param string $code
+     * @return \Illuminate\Support\Collection|null
+     */
+    public function getPosInventoryByWarehouseCode(string $code)
+    {
+        $warehouse = Warehouse::where('code', $code)->first();
+
+        if (!$warehouse) {
+            return null;
+        }
+
+        // 整理該倉庫的庫存，以 product_id 進行 GROUP BY 並加總 quantity
+        return DB::table('inventories')
+            ->join('products', 'inventories.product_id', '=', 'products.id')
+            ->where('inventories.warehouse_id', $warehouse->id)
+            ->whereNull('inventories.deleted_at')
+            ->whereNull('products.deleted_at')
+            ->select(
+                'products.external_pos_id',
+                'products.code as product_code',
+                'products.name as product_name',
+                DB::raw('SUM(inventories.quantity) as total_quantity')
+            )
+            ->groupBy('inventories.product_id', 'products.external_pos_id', 'products.code', 'products.name')
+            ->get();
+    }
 }