Adds a dedicated Docker environment for reviewing untrusted pull requests
with codex/claude, keeping CLI auth state in volumes and using a separate
scratch workspace for PR checkouts.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Rewrites Dockerfile to use bookworm-slim base, installs Claude and Codex
CLIs, adds docker-compose.quickstart.yml for one-command setup, and adds
DOCKER.md with usage instructions.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>