feat(weixin): native official runner and OSS install docs

Default Weixin to official native runner, add /weixin/native/reply host endpoint, and harden gateway stop to clean stale port listeners.
Document open-source installation flow for gateway + Personal WeChat.

Made-with: Cursor

runtime/operations/scripts/weixin_stop.ps1

@@ -24,6 +24,7 @@ function Get-SidecarProcesses {
   $patterns = @(
     "*$ChannelId*",
     "*runner.ts*",
+    "*official_runner.ts*",
     "*$escapedSidecarRoot*"
   )
   Get-CimInstance Win32_Process | Where-Object {