feat: easy self-deployment with Dockerfile and Docker Compose

[manojbajaj95]

Summary

Add a Dockerfile and docker-compose.yml so users can self-host the authsome daemon with a single command, plus a deployment guide covering common setups.

Motivation

Running authsome locally today requires installing Python, uv, and the package. For teams or servers that want a persistent credential daemon (e.g. backing a CI runner or a shared agent host), a containerised deployment is far easier to manage, upgrade, and monitor.

Proposed Additions

Dockerfile

• Multi-stage build: uv builder stage → slim runtime image.
• Runs the authsome daemon as a non-root user.
• Exposes port 7998 (daemon HTTP).
• Mounts ~/.authsome (or /data/authsome) as a named volume so credentials survive container restarts.

docker-compose.yml

• Single authsome service using the above image.
• Named volume for AUTHSOME_HOME.
• restart: unless-stopped.
• Optional traefik / caddy sidecar snippet for TLS termination (commented out).

Deployment guide (docs/guides/self-hosting.md)

• Quick-start: docker compose up -d and point AUTHSOME_DAEMON_URL at the container.
• Volume backup and restore instructions.
• Upgrading to a new image version.
• Environment variables reference (AUTHSOME_HOME, AUTHSOME_LOG_LEVEL, encryption mode, etc.).

Work Items

• Write Dockerfile (multi-stage, non-root, uv-based)
• Write docker-compose.yml with named volume and restart policy
• Add docs/guides/self-hosting.md deployment guide
• Add a .dockerignore
• CI: add a Docker build job to verify the image builds on every PR
• Update README.md with a self-hosting quick-start section