perf(portable): U盘启动加速 — 缓存搬本机 + 启动首屏 + 首轮预热

便携版从 U 盘启动慢,瓶颈在 U 盘随机小写 IO + 首屏无反馈 + 首轮冷启动。
移植 v2 u-clawx 4.0 的 4 个可在纯脚本层复刻的手段(均零依赖、静默失败):

- portable-cache.mjs: 把浏览器 user-data(几百 MB 随机小写)+ V8 编译缓存
  从 U 盘搬到本机 SSD(win junction / mac symlink 重定向 .openclaw/browser,
  NODE_COMPILE_CACHE 落本机)。UUID 隔离让换盘符仍命中同一份缓存。
  业务数据(openclaw.json/memory/账号)仍留 U 盘,便携性不变。
- loading.html: 双击即弹的启动首屏,自轮询 /ready,gateway 真就绪后自动跳
  Dashboard——天然规避"gateway 没起就开 Dashboard 拒连"(issue #46/#48)。
- prewarm.mjs: gateway 首轮预热,后台静默唤醒 config/model 子系统。
- Windows-Start.bat: 等 config-server 改写死 timeout 为动态轮询 18788。
- wait-gateway.bat 退居兜底(首屏页负责主跳转)。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

portable/lib/wait-gateway.bat

@@ -3,6 +3,10 @@ REM wait-gateway.bat - open Dashboard only after the Gateway is actually listeni
 REM Fixes issue #46/#48: on slow USB drives the gateway needs tens of seconds to
 REM stage bundled deps on first run; opening http://127.0.0.1:PORT before it is
 REM LISTENING shows "connection refused" and users think it is broken.
+REM
+REM 角色变更：现在 Windows-Start.bat 会先开 lib\loading.html 启动首屏，由首屏
+REM 自己轮询 /ready 并自动跳 Dashboard。本脚本退居"兜底"——万一首屏页的
+REM file:// fetch 被浏览器拦住没跳成，这里仍轮询端口、就绪后开 Dashboard。
 REM Usage (called in background by Windows-Start.bat): wait-gateway.bat PORT
 REM Polls every 2s, up to 150 tries (~5 min). Opens the browser once ready.