refactor: 员工同步复用钉钉免密登录配置

- 移除员工同步独立的 API 凭证配置
- 复用 dingtalk 配置组的 CorpId、AppKey、AppSecret
- 简化前端界面，只保留开关和测试连接

backend/app/services/employee_sync_service.py

@@ -29,17 +29,18 @@ class EmployeeSyncService:
         self._dingtalk_config = None
     
     async def _get_dingtalk_config(self) -> Dict[str, str]:
-        """从数据库获取钉钉 API 配置"""
+        """从数据库获取钉钉 API 配置（复用免密登录配置）"""
         if self._dingtalk_config:
             return self._dingtalk_config
         
         try:
+            # 从 dingtalk 配置组读取（与免密登录共用）
             result = await self.db.execute(
                 text("""
                     SELECT config_key, config_value 
                     FROM tenant_configs 
                     WHERE tenant_id = :tenant_id 
-                    AND config_group = 'employee_sync'
+                    AND config_group = 'dingtalk'
                 """),
                 {"tenant_id": self.tenant_id}
             )
@@ -47,7 +48,13 @@ class EmployeeSyncService:
             
             config = {}
             for key, value in rows:
-                config[key] = value
+                # 转换 key 名称以匹配 DingTalkService 需要的格式
+                if key == 'DINGTALK_CORP_ID':
+                    config['CORP_ID'] = value
+                elif key == 'DINGTALK_APP_KEY':
+                    config['CLIENT_ID'] = value
+                elif key == 'DINGTALK_APP_SECRET':
+                    config['CLIENT_SECRET'] = value
             
             self._dingtalk_config = config
             return config