Prefer Chromium for turnstilePatch on headless servers

Google Chrome blocks --load-extension, so CF tokens stay empty under
Xvfb. Auto-select Chromium when the extension is present, install/
detect chromium in start.sh, and document browser_prefer overrides.

config.example.json

@@ -56,9 +56,11 @@
   "// ===== 网络 / 浏览器 =====": "",
   "// proxy": "注册机主代理：Chromium + 邮箱 HTTP。可带账号 http://user:pass@host:port。优先于系统 https_proxy。",
   "proxy": "http://127.0.0.1:7890",
-  "// browser_headless": "注册 Chromium：true=强制无头，false=强制有头，auto/省略=无 DISPLAY 时自动 headless。也可用 env BROWSER_HEADLESS / CLI --headless|--headed。无头服务器建议 xvfb-run。",
+  "// browser_headless": "注册浏览器：true=强制无头，false=强制有头，auto/省略=无 DISPLAY 时自动 headless。也可用 env BROWSER_HEADLESS / CLI --headless|--headed。无头服务器建议 start.sh 自动 Xvfb。",
   "browser_headless": "auto",
-  "// browser_path": "可选，强制 Chromium/Chrome 可执行文件路径；默认自动探测 google-chrome-stable / chromium。",
+  "// browser_prefer": "auto=有 turnstilePatch 时优先 Chromium（可 --load-extension）；chromium|chrome 强制偏好。Google Chrome 无法加载扩展，服务器上 Turnstile 常 token=0。",
+  "browser_prefer": "auto",
+  "// browser_path": "可选，强制浏览器可执行文件路径；默认按 browser_prefer 自动探测。",
   "browser_path": "",
   "// user_agent": "Chromium UA；一般保持默认 Chrome 桌面串即可。",
   "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36",