Initial version of fail2ban-webui

Web interface to view, ban and unban fail2ban IPs on several hosts via
SSH, generalised from the private f2b-web tool.

- Web UI (Flask/Waitress): hosts.yaml, local/OIDC/proxy authentication,
  English/German UI, origin map, optional Loki/Grafana/GeoIP, CLI helpers
- Agent f2b-webctl with install.sh/uninstall.sh (dedicated user + sudo,
  from= restriction, protected networks, manual jail)
- Hardened Docker image, examples, documentation, smoke test, testbed

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

requirements.txt

@@ -0,0 +1,6 @@
+flask==3.1.3
+waitress==3.0.2
+maxminddb==3.2.0
+PyYAML==6.0.3
+Authlib==1.6.12
+requests==2.34.2