Add bridge maintenance cleanup to detect reverse tunnels whose remote
port is bound but no longer forwards (zombie sshd sessions), kill the
stale listeners on the remote host, and optionally restart the tunnel.
Includes install-cron/uninstall-cron/show-cron helpers and README notes
for the actcore-state-hub-bridge failure mode we hit on railiance01.
Document ClientAliveInterval/ClientAliveCountMax requirement on remote
sshd to prevent stale sessions holding ports after reconnect. Document
fail2ban ignoreip setup. Clarify that health_check.url must be a local
port (not the remote forwarded port), and that SSE endpoints block the
health checker.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
