Auto headless + Xvfb for headless servers

Enable Chromium on machines without DISPLAY: Python auto headless
with Xvfb hints, and start.sh installs/starts Xvfb (xvfb-run or
persistent :99) so registration can run headed under a virtual display.

config.example.json

@@ -56,6 +56,10 @@
   "// ===== 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": "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_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",
   "// enable_nsfw": "注册成功后是否尝试打开 NSFW（历史字段；与 CPA 无关）",
@@ -145,7 +149,7 @@
   "cpa_base_url": "https://cli-chat-proxy.grok.com/v1",
   "// cpa_proxy": "OIDC mint 专用代理（device-code/token/probe/浏览器）。优先级: cpa_proxy > proxy > 环境 https_proxy。空=用 proxy。",
   "cpa_proxy": "http://127.0.0.1:7890",
-  "// cpa_headless": "device 确认浏览器是否无头。accounts.x.ai 建议 false（有头）",
+  "// cpa_headless": "回退浏览器是否无头。false=有头（推荐，过 CF 更稳）；true=无头；省略/auto 时无 DISPLAY 自动无头。无显示时即使 false 也会强制 headless 以免起不来。",
   "cpa_headless": false,
   "// cpa_force_standalone": "true=新开 Chromium+turnstilePatch 做 OIDC；勿复用注册 tab",
   "cpa_force_standalone": true,