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

go.mod

@@ -0,0 +1,16 @@
+module git.hangman-lab.top/zhi/HarborForge.Monitor
+
+go 1.22
+
+require github.com/shirou/gopsutil/v4 v4.25.2
+
+require (
+	github.com/ebitengine/purego v0.8.2 // indirect
+	github.com/go-ole/go-ole v1.2.6 // indirect
+	github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 // indirect
+	github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c // indirect
+	github.com/tklauser/go-sysconf v0.3.12 // indirect
+	github.com/tklauser/numcpus v0.6.1 // indirect
+	github.com/yusufpapurcu/wmi v1.2.4 // indirect
+	golang.org/x/sys v0.28.0 // indirect
+)