Harden against bot floods and add post-provisioning service check

- Traefik rate-limits all routes (60 req/min standard, 300 for Nextcloud)
  and writes access logs to /var/log/traefik/access.log
- Fail2ban watches Traefik access logs and bans IPs after 10 x 403/404
  within 60 s for 24 h
- Nextcloud html directory created as www-data (UID 33) so Apache can
  process .htaccess and serve requests correctly
- scripts/check-services.sh verifies all seven endpoints return the
  expected HTTP status after provisioning

ansible/roles/mail/templates/docker-compose.yml.j2

@@ -49,6 +49,7 @@ services:
       - "traefik.http.routers.mail.entrypoints=websecure"
       - "traefik.http.routers.mail.tls.certresolver=letsencrypt"
       - "traefik.http.services.mail.loadbalancer.server.port=80"
+      - "traefik.http.routers.mail.middlewares=rate-limit@docker"
     depends_on:
       mail-db:
         condition: service_healthy