Add Gmail+Email Worker hybrid mail path and private runtime config

Prefer Cloudflare Worker KV for verification codes with optional short IMAP
fallback disabled for private deploy; track config.json/.env for private repo.
Also add worker project, protocol mint backoff, and fail-fast Turnstile/mail
timeouts from batch runs.

config.example.json

@@ -187,6 +187,22 @@
   "gmail_imap_password": "",
   "gmail_imap_host": "imap.gmail.com",
   "gmail_imap_port": 993,
+  "// gmail_worker_enabled": "true=优先用 Cloudflare Email Worker HTTP 取码（秒级）；false=仅 IMAP",
+  "gmail_worker_enabled": false,
+  "// gmail_worker_url": "Worker 根 URL，如 https://grok-xai-mail-codes.<subdomain>.workers.dev",
+  "gmail_worker_url": "",
+  "// gmail_worker_api_key": "与 Worker 环境变量 CODE_API_KEY 相同",
+  "gmail_worker_api_key": "",
+  "// gmail_worker_timeout_sec": "Worker 轮询最长秒数，超时后若 gmail_imap_fallback=true 则回退 IMAP",
+  "gmail_worker_timeout_sec": 25,
+  "// gmail_worker_poll_interval": "Worker HTTP 轮询间隔（秒）",
+  "gmail_worker_poll_interval": 0.4,
+  "// gmail_imap_fallback": "Worker 未命中时是否回退 Gmail IMAP",
+  "gmail_imap_fallback": true,
+  "// gmail_imap_fallback_timeout_sec": "Worker 未命中后 IMAP 最多等几秒（Catch-all 只进 Worker 时请设小或关闭 fallback）",
+  "gmail_imap_fallback_timeout_sec": 30,
+  "// gmail_worker_timeout_sec": "Worker 轮询最长秒数；命中通常 1–3s，过大只会拖慢换号",
+  "gmail_worker_timeout_sec": 12,
   "// 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",