docs(readme): 调试模式用 gateway run（前台）非 gateway start

[bigbrother666sh]

核实 openclaw 源码（src/cli/daemon-cli/register-service-commands.ts）：
gateway start/stop/restart 走 launchd/systemd/schtasks 服务管理；
gateway run（src/cli/gateway-cli/register.ts:519 "Run the WebSocket Gateway (foreground)"）才是前台单次启动。

原 README「调试模式（单次启动，适合测试）：gateway start」把服务启动命令当成前台调试，在 managed install 下会启服务（和 launchd 打架/重复启）而非前台跑。改成 gateway run。

换绑流程里的 gateway stop / gateway start 是对的（清完 weixin 数据后重启服务），不动。

Auto Release 已禁用，不 bump 版本，保持 v5.6.0。README 走 raw URL，无需重建 tarball。

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