fix(portable): gateway 启动卡死/Dashboard 拒连 (issue #46/#48)

根因：Windows-Start.bat 在 gateway 启动【前】就打开 http://127.0.0.1:18789，
而慢 U 盘上 OpenClaw 首次启动要几十秒 staging bundled deps，浏览器打开时
端口还没监听 → "127.0.0.1 拒绝连接"，用户以为坏了。

修复：
- 新增 lib/wait-gateway.bat：后台轮询端口(每2s,最多~5min)，gateway 真正
  LISTENING 后才打开 Dashboard；超时回退到 Config Center。
- Windows-Start.bat：移除 gateway 启动前的过早开浏览器，改由 wait-gateway
  在 ready 后触发；加"首次启动需 30-90 秒"的明确提示。
- Mac-Start.command 本就先轮询 curl 再开浏览器，无此问题。

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

portable/lib/wait-gateway.bat

@@ -0,0 +1,28 @@
+@echo off
+REM wait-gateway.bat - open Dashboard only after the Gateway is actually listening.
+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 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.
+
+set "PORT=%~1"
+if "%PORT%"=="" set "PORT=18789"
+
+set /a TRIES=0
+:wait_loop
+netstat -an | findstr ":%PORT% " | findstr "LISTENING" >nul 2>&1
+if %errorlevel%==0 goto :ready
+set /a TRIES+=1
+if %TRIES% geq 150 goto :timeout
+timeout /t 2 /nobreak >nul
+goto :wait_loop
+
+:ready
+timeout /t 1 /nobreak >nul
+start "" http://127.0.0.1:%PORT%/#token=uclaw
+exit /b 0
+
+:timeout
+start "" http://127.0.0.1:18788/
+exit /b 1