Track agent.heartbeat and report.daily.ssh per host; show online/stale on Hosts UI; dashboard counters and SAC_HEARTBEAT_STALE_MINUTES config.
Centralize APP_VERSION 0.2.0; /health and /healthz return version; startup log line; UI title Security Alert Center v.0.2.0; SSE /api/v1/stream/events for live dashboard counters.