feat: restore traefik to prod compose and add standalone traefik compose

- Add Traefik v3.2 service back to docker-compose.prod.yml with:
  - Dashboard with basic auth middleware
  - Let's Encrypt TLS challenge
  - HTTP→HTTPS redirect
  - Health checks and structured logging
- Create docker-compose.traefik.yml for standalone Traefik deployment:
  - Mirrors production Traefik configuration
  - Isolated network for external proxy usage
  - Persistent certificate storage
- Add TRAEFIK_ACME_EMAIL to .env.example
- All compose files validated with docker compose config

.env.example

@@ -26,6 +26,7 @@ TRAEFIK_NETWORK=traefik
 TRAEFIK_ENTRYPOINT=websecure
 TRAEFIK_CERT_RESOLVER=letsencrypt
 TRAEFIK_LOG_LEVEL=INFO
+TRAEFIK_ACME_EMAIL=admin@example.com
 TOOL_SUBDOMAIN_PATTERN={tool}-{project}-{user}.tools.localhost
 
 # Frontend build-time variables (passed to web container)