- Add Caddyfile: proxies to explorer:3001, domain set via $DOMAIN env var
- docker-compose: new caddy service (ports 80/443/443-udp), persistent
caddy_data/caddy_config volumes; remove direct explorer port binding
- .env.example: replace EXPLORER_PORT with DOMAIN
Set DOMAIN=localhost for local dev (HTTP), DOMAIN=your.domain.com for
production (Caddy fetches Let's Encrypt cert automatically)
