[AI] Update WebSocket async docs

[ishaanlabs-gg]

Update the WebSocket section of the asynchronous applications docs with the guidance from #1464:

• add the missing gevent.monkey.patch_all() call before importing Bottle
• mention the geventwebsocket.gunicorn.workers.GeventWebSocketWorker Gunicorn worker
• describe running a separate WebSocket service behind a reverse proxy when the Bottle app should stay WSGI-only

AI disclosure and review:

• This PR was prepared with AI assistance from OpenAI Codex (GPT-5).
• I manually reviewed the issue discussion, the repository AGENTS.md, and the final diff before submitting.
• I license my contribution in this PR as public domain.

Validation:

• /Volumes/STOREJET/2/Dependencies/bottle-docs-venv/bin/python -m sphinx -b html docs build/docs-html
• /Volumes/STOREJET/2/Dependencies/bottle-docs-venv/bin/python -m docutils docs/async.rst
• git diff --check

Notes:

• I also ran /Volumes/STOREJET/2/Dependencies/bottle-docs-venv/bin/python -m sphinx -W -b html docs build/docs-html. It read docs/async.rst successfully, then failed on existing warnings in docs/api.rst about cached property signatures and a malformed table; those are outside this PR.

Fixes #1464