Self-hosted LiveKit server compose profile

## Summary

Roadmap v1.2: self-hosted LiveKit server compose profile. Today we have a `livekit-worker` profile that expects Cloud or an external server.

## Context

- `docker-compose.prod.yml` `livekit-worker`
- `docs/release/known-limitations.md`
- ADR-004

## Scope

- [ ] Optional compose profile that runs LiveKit server locally
- [ ] Document keys, ports, and how the worker joins
- [ ] Do not make it default (resource-heavy)
- [ ] Smoke: token endpoint + worker starts

## Notes

Follow existing profile patterns (`livekit`, `monitoring`). Prefer official LiveKit images.

Start with the livekit-worker profile in docker-compose.prod.yml, then read the livekit and monitoring profile patterns, ADR-004, and docs/release/known-limitations.md. Define the optional local-server profile without making it default, document its keys, ports, and worker connection, and verify the token endpoint and worker startup smoke checks.

Written by the indexing model from the issue text.