AtAuth

Add Docker support and homelab deployment documentation master

- Add multi-stage Dockerfile for gateway with non-root user and health checks - Add docker-compose.yml with Traefik labels and volume persistence - Add GitHub Actions workflow for building/pushing to ghcr.io (multi-arch) - Add comprehensive HOMELAB.md deployment guide with reverse proxy examples - Update README.md to emphasize self-hosted PDS as primary use case - Add .env.example with configuration template