Delete verification emails after code extraction

IMAP-delete Gmail/Hotmail verification messages once the code is parsed, with config toggles and non-blocking failure handling.

config.example.json

@@ -186,5 +186,9 @@
   "// gmail_imap_password": "Gmail 应用专用密码（非登录密码）",
   "gmail_imap_password": "",
   "gmail_imap_host": "imap.gmail.com",
-  "gmail_imap_port": 993
+  "gmail_imap_port": 993,
+  "// gmail_delete_after_code": "Gmail 取到验证码后是否 IMAP 删除该邮件（失败不影响注册）",
+  "gmail_delete_after_code": true,
+  "// hotmail_delete_after_code": "Hotmail/Outlook 取到验证码后是否 IMAP 删除该邮件",
+  "hotmail_delete_after_code": true
 }