feat: Update mail service implementation and its configuration example.

config.toml.example

@@ -19,15 +19,14 @@ allowed_users = []                  # 允许使用的用户ID列表（空=不限
 
 # --- 邮箱系统（轮询使用，API 接口相同）---
 # 可添加多个 [[mail]] 块
+# api_token: 直接配置 API Token，无需管理员账号密码
 
 [[mail]]
 base_url = "https://mail.example.com/"
-admin_email = "admin@example.com"
-admin_pass = "your_password"
+api_token = "your_api_token_here"
 domains = ["example.com"]
 
 # [[mail]]
 # base_url = "https://mail2.example.com/"
-# admin_email = "admin@mail2.example.com"
-# admin_pass = "pass2"
+# api_token = "your_api_token_here"
 # domains = ["domain2.com", "domain3.com"]