Configure docker-compose for Coolify/Traefik deployment

Replace the host-port-published nginx service with one that joins an
external Docker network and routes entirely through Traefik labels
(HTTP->HTTPS redirect, TLS router, security-headers middleware), matching
the pattern used by other Coolify-deployed projects. Add .env.example for
TRAEFIK_ENABLED/TRAEFIK_HOST/NETWORK_NAME and document the new deploy flow
and local-preview alternative in the README.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,4 @@
+# Traefik (set TRAEFIK_ENABLED=true when deploying behind Traefik, e.g. via Coolify)
+TRAEFIK_ENABLED=false
+TRAEFIK_HOST=vpinball.example.com
+NETWORK_NAME=traefik-network