Docs: tested single-host install, NPM integration, installer --docker

- README: step-by-step installation of web UI and agent on one host,
  exactly as tested (agent after keygen, all "run" helpers before
  "up -d", http PUBLIC_URL and TRUSTED_PROXY_HOPS=0 without a proxy)
- README: attach to an existing Nginx Proxy Manager in Docker – shared
  network via docker-compose.override.yaml, no published port,
  gw_priority so SSH to the agent keeps the source address of the own
  network (otherwise from= rejects it), TLS settings, test
- install.sh --docker: the new manual jail bans in INPUT and DOCKER-USER
- Running container: helpers via "docker compose exec … python -m webui"
  (run fails with "Address already in use"); troubleshooting entries

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/configuration.md

@@ -21,9 +21,9 @@ hosts:
 Nach dem Hinzufügen eines Hosts `keyscan` erneut ausführen, dann neu starten:
 
 ```bash
-docker compose run --rm -it fail2ban-webui keyscan
-docker compose run --rm fail2ban-webui check
-docker compose up -d --force-recreate
+docker compose exec -it fail2ban-webui python -m webui keyscan
+docker compose exec fail2ban-webui python -m webui check
+docker compose restart
 ```
 
 `F2B_HOSTS=name=adresse,name2=adresse2` (Port 22, Benutzer `SSH_USER`) wird aus