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>

dev/testbed/agent/Dockerfile

@@ -0,0 +1,36 @@
+# syntax=docker/dockerfile:1
+# Test host: sshd + fail2ban (dummy actions, no firewall changes).
+# The agent is installed at start with agent/install.sh – exactly like on a real host.
+# Build context: repository root (see ../docker-compose.yaml)
+FROM debian:trixie-slim
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends openssh-server openssh-client fail2ban python3 sudo iproute2 \
+ && rm -rf /var/lib/apt/lists/* /etc/fail2ban/jail.d/* /etc/ssh/ssh_host_* \
+ && mkdir -p /run/sshd && touch /var/log/empty.log
+
+COPY <<'JAIL' /etc/fail2ban/jail.local
+[DEFAULT]
+banaction = dummy
+banaction_allports = dummy
+backend = polling
+
+[sshd]
+enabled = true
+logpath = /var/log/empty.log
+JAIL
+
+COPY agent/ /opt/fail2ban-webui-agent/
+
+COPY <<'ENTRY' /entrypoint.sh
+#!/bin/sh
+set -e
+ssh-keygen -A >/dev/null
+until [ -s /keys/ssh/id_ed25519.pub ]; do echo "waiting for /keys/ssh/id_ed25519.pub"; sleep 2; done
+fail2ban-client -x start >/dev/null
+# INSTALL_ARGS: options for install.sh, set per agent in docker-compose.yaml
+bash /opt/fail2ban-webui-agent/install.sh --yes --key-file /keys/ssh/id_ed25519.pub $INSTALL_ARGS
+for ip in $SAMPLE_BANS; do fail2ban-client set sshd banip "$ip" >/dev/null; done
+exec /usr/sbin/sshd -D -e
+ENTRY
+RUN chmod 0755 /entrypoint.sh
+ENTRYPOINT ["/entrypoint.sh"]