mc-heartbeat-mc-dispatcher-are-systemd-not-cron

Both mc-heartbeat and mc-dispatcher run as systemd services, not crontab entries. Architecture.md and the enterprise skill must reflect this — listing them under cron jobs creates operational confusion. The dispatcher resolves agent IDs dynamically via the MC API at startup (name→id caching) to avoid brittle hardcoded integer IDs that break when agents are re-registered.