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/scripts/install.sh

@@ -0,0 +1,47 @@
+#!/bin/sh
+set -eu
+
+SERVICE="mcns"
+BINARY="/usr/local/bin/mcns"
+DATA_DIR="/srv/${SERVICE}"
+UNIT_DIR="/etc/systemd/system"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_DIR="$(cd "${SCRIPT_DIR}/../.." && pwd)"
+
+# Create system user and group (idempotent).
+if ! id -u "${SERVICE}" >/dev/null 2>&1; then
+    useradd --system --no-create-home --shell /usr/sbin/nologin "${SERVICE}"
+    echo "Created system user ${SERVICE}."
+fi
+
+# Install binary.
+install -m 0755 "${REPO_DIR}/mcns" "${BINARY}"
+echo "Installed binary."
+
+# Create data directory structure.
+install -d -o "${SERVICE}" -g "${SERVICE}" -m 0700 "${DATA_DIR}"
+install -d -o "${SERVICE}" -g "${SERVICE}" -m 0700 "${DATA_DIR}/backups"
+install -d -o "${SERVICE}" -g "${SERVICE}" -m 0700 "${DATA_DIR}/certs"
+echo "Created ${DATA_DIR}/."
+
+# Install example config if none exists.
+if [ ! -f "${DATA_DIR}/${SERVICE}.toml" ]; then
+    install -o "${SERVICE}" -g "${SERVICE}" -m 0600 \
+        "${REPO_DIR}/deploy/examples/mcns.toml" \
+        "${DATA_DIR}/${SERVICE}.toml"
+    echo "Installed example config to ${DATA_DIR}/${SERVICE}.toml — edit before starting."
+fi
+
+# Install systemd units.
+install -m 0644 "${REPO_DIR}/deploy/systemd/${SERVICE}.service" "${UNIT_DIR}/"
+install -m 0644 "${REPO_DIR}/deploy/systemd/${SERVICE}-backup.service" "${UNIT_DIR}/"
+install -m 0644 "${REPO_DIR}/deploy/systemd/${SERVICE}-backup.timer" "${UNIT_DIR}/"
+systemctl daemon-reload
+echo "Installed systemd units."
+
+echo ""
+echo "Done. Next steps:"
+echo "  1. Edit ${DATA_DIR}/${SERVICE}.toml"
+echo "  2. Place TLS certs in ${DATA_DIR}/certs/"
+echo "  3. systemctl enable --now ${SERVICE}"
+echo "  4. systemctl enable --now ${SERVICE}-backup.timer"

deploy/systemd/mcns-backup.service

@@ -0,0 +1,25 @@
+[Unit]
+Description=MCNS Database Backup
+
+[Service]
+Type=oneshot
+User=mcns
+Group=mcns
+ExecStart=/usr/local/bin/mcns snapshot --config /srv/mcns/mcns.toml
+ExecStartPost=/usr/bin/find /srv/mcns/backups -name 'mcns-*.db' -mtime +30 -delete
+
+# Security hardening
+NoNewPrivileges=true
+ProtectSystem=strict
+ProtectHome=true
+PrivateTmp=true
+PrivateDevices=true
+ProtectKernelTunables=true
+ProtectKernelModules=true
+ProtectControlGroups=true
+RestrictSUIDSGID=true
+RestrictNamespaces=true
+LockPersonality=true
+MemoryDenyWriteExecute=true
+RestrictRealtime=true
+ReadWritePaths=/srv/mcns

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

deploy/systemd/mcns.service

@@ -0,0 +1,34 @@
+[Unit]
+Description=MCNS Networking Service
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=mcns
+Group=mcns
+ExecStart=/usr/local/bin/mcns server --config /srv/mcns/mcns.toml
+Restart=on-failure
+RestartSec=5
+
+# Security hardening
+NoNewPrivileges=true
+ProtectSystem=strict
+ProtectHome=true
+PrivateTmp=true
+PrivateDevices=true
+ProtectKernelTunables=true
+ProtectKernelModules=true
+ProtectControlGroups=true
+RestrictSUIDSGID=true
+RestrictNamespaces=true
+LockPersonality=true
+MemoryDenyWriteExecute=true
+RestrictRealtime=true
+ReadWritePaths=/srv/mcns
+
+# Allow binding to privileged ports (DNS port 53)
+AmbientCapabilities=CAP_NET_BIND_SERVICE
+
+[Install]
+WantedBy=multi-user.target