fix: 修复飞书卡片回调JSON编码问题，解决200671错误

- 添加 JSON_UNESCAPED_UNICODE 防止中文被转义
- 添加 JSON_UNESCAPED_SLASHES 防止斜杠被转义
- Content-Type 添加 charset=utf-8

backend/app/controller/FeishuCardController.php

@@ -419,8 +419,8 @@ class FeishuCardController extends BaseController
     {
         return new \Webman\Http\Response(
             200,
-            ['Content-Type' => 'application/json'],
+            ['Content-Type' => 'application/json; charset=utf-8'],
-            json_encode($data)
+            json_encode($data, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES)
         );
     }
 }