feat: add Go-based HarborForge monitor client

- collect CPU, memory, disk, swap, load, and uptime telemetry
- detect nginx and list /etc/nginx/sites-enabled entries
- send heartbeat-v2 payload with API key auth
- provide install script, config example, and systemd unit

systemd/harborforge-monitor.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=HarborForge Monitor Telemetry Client
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=root
+WorkingDirectory=/etc/harborforge-monitor
+ExecStart=/usr/local/bin/harborforge-monitor -config /etc/harborforge-monitor/config.json
+Restart=always
+RestartSec=10
+
+[Install]
+WantedBy=multi-user.target