Add WeChat (Weixin) gateway support

[halmisen]

Summary

This adds WeChat (Weixin) support to the gateway through the official iLink Bot API.

The main pieces are:

• a new Weixin gateway adapter
• a hermes wechat QR login flow
• config, setup, status, and send-message wiring for WeChat
• regression tests to make sure this coexists cleanly with the existing BlueBubbles path

Notes

I had a local Weixin integration working already, but the first pass made it pretty clear that shared gateway plumbing is easy to break when a new platform gets added. In particular, this needed to land without knocking out existing platforms that still rely on the same enum and config paths.

This version ports the Weixin work onto current main and keeps the existing BlueBubbles support in place instead of replacing it.

Validation

• python -m py_compile gateway/platforms/weixin.py hermes_cli/wechat_login.py scripts/weixin_login.py hermes_cli/main.py hermes_cli/gateway.py hermes_cli/config.py gateway/config.py gateway/run.py tools/send_message_tool.py
• pytest tests/gateway/test_weixin_config.py tests/gateway/test_bluebubbles.py -q
• pytest tests/gateway/test_allowlist_startup_check.py tests/gateway/test_status.py tests/gateway/test_internal_event_bypass_pairing.py -q

[teknium1]

Merged via PR #8665 which synthesizes the best fixes from ~25 community PRs into a single consolidated change. Your contribution (WeChat gateway support) was reviewed and informed the final implementation. Thank you @halmisen for your work on this!