Add systemd units and install script for MCNS deployment

Ship mcns.service, mcns-backup.service, mcns-backup.timer, and
deploy/scripts/install.sh adapted from MCR's deployment files.
Includes full security hardening block per engineering standards
and AmbientCapabilities=CAP_NET_BIND_SERVICE for DNS port 53.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/systemd/mcns-backup.timer

@@ -0,0 +1,10 @@
+[Unit]
+Description=MCNS Daily Database Backup
+
+[Timer]
+OnCalendar=*-*-* 02:00:00 UTC
+RandomizedDelaySec=300
+Persistent=true
+
+[Install]
+WantedBy=timers.target