feat(rego-tunnel): Add Dockerfile and build scripts for cisco-vpn image

Includes:
- Dockerfile for native Cisco Secure Client in Docker
- Build scripts (init-vpn.sh, startup-vnc.sh, vpn-connect.sh)
- VNC configuration (xstartup, vnc.service)
- build.sh for manual image builds
- README documenting the architecture

Note: cisco-secure-client-full.tar.gz is gitignored (large binary)
Copy it from ~/projects/cisco-vpn/build/ before building.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/rego-tunnel/build/scripts/xstartup

@@ -0,0 +1,21 @@
+#!/bin/bash
+# VNC xstartup - launches window manager and VPN UI
+
+unset SESSION_MANAGER
+unset DBUS_SESSION_BUS_ADDRESS
+
+export XDG_RUNTIME_DIR=/tmp/runtime-root
+mkdir -p $XDG_RUNTIME_DIR
+chmod 700 $XDG_RUNTIME_DIR
+
+# Start dbus session
+[ -x /usr/bin/dbus-launch ] && eval $(dbus-launch --sh-syntax --exit-with-session)
+
+# Start window manager
+openbox &
+sleep 2
+
+# Start Cisco VPN UI
+/opt/cisco/secureclient/bin/vpnui &
+
+wait