Remote deployment documentation

[omoshola-o]

Create docs/remote-deployment.md covering:

1. Single VPS setup (Hetzner, DigitalOcean, etc.)
2. Docker container
3. Nginx reverse proxy with TLS
4. Caddy auto-TLS alternative
5. Systemd service file
6. Multi-tenant configuration
7. Backup strategies
8. Monitoring with /health endpoint

Part of #1