feat(oam): add LibreNMS agent deployment
Implement comprehensive check_mk agent deployment for LibreNMS monitoring:
- Create agent directory structure (/usr/lib/check_mk_agent/plugins, local, etc.)
- Deploy main check_mk_agent binary to /usr/bin
- Deploy distro script for OS detection
- Install systemd socket activation (check_mk.socket, check_mk@.service)
- Deploy monitoring plugins (smart, ntp-client, ntp-server, os-updates, postfix)
- Configure and enable check_mk socket for immediate monitoring
This enables centralised infrastructure monitoring through LibreNMS with
hardware health, NTP synchronisation, and mail queue visibility.
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