Make Weixin launch scripts portable on Windows - #23

What changed

• Run the Weixin login and service commands through the repository's local tsx entrypoint.
• Resolve node.exe and codex.exe from PATH instead of hard-coding user- and version-specific executable paths.
• Preserve preconfigured environment overrides and use %USERPROFILE%\Documents as the portable default working directory.
• Keep Weixin state under the repository-local .codexbridge directory.

Why

The previous launch scripts depended on one developer's npm-installed Codex command and absolute document path. Those assumptions fail on Codex desktop installations and on other Windows user profiles.

Impact

Windows users can launch Weixin login and serving with the local project dependencies while retaining the option to override Node, Codex, locale, transport, and working-directory settings through environment variables.

Validation

• git diff --check
• Confirmed where node.exe and where codex.exe resolve successfully from cmd.exe
• npm.cmd run typecheck was attempted; it remains blocked by pre-existing codex-provider-relay example and test type errors unrelated to these batch scripts