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

internal/telemetry/telemetry.go

@@ -0,0 +1,158 @@
+package telemetry
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+
+	"github.com/shirou/gopsutil/v4/cpu"
+	"github.com/shirou/gopsutil/v4/disk"
+	"github.com/shirou/gopsutil/v4/host"
+	gopsload "github.com/shirou/gopsutil/v4/load"
+	"github.com/shirou/gopsutil/v4/mem"
+
+	"git.hangman-lab.top/zhi/HarborForge.Monitor/internal/config"
+)
+
+const Version = "0.1.0"
+
+type Payload struct {
+	Identifier     string    `json:"identifier"`
+	PluginVersion  string    `json:"plugin_version,omitempty"`
+	Agents         []any     `json:"agents"`
+	NginxInstalled bool      `json:"nginx_installed"`
+	NginxSites     []string  `json:"nginx_sites"`
+	CPUPct         float64   `json:"cpu_pct,omitempty"`
+	MemPct         float64   `json:"mem_pct,omitempty"`
+	DiskPct        float64   `json:"disk_pct,omitempty"`
+	SwapPct        float64   `json:"swap_pct,omitempty"`
+	LoadAvg        []float64 `json:"load_avg,omitempty"`
+	UptimeSeconds  uint64    `json:"uptime_seconds,omitempty"`
+}
+
+func BuildPayload(ctx context.Context, cfg config.Config) (Payload, error) {
+	payload := Payload{
+		Identifier:    cfg.Identifier,
+		PluginVersion: Version,
+		Agents:        []any{},
+		NginxSites:    []string{},
+	}
+
+	cpuPct, err := cpu.PercentWithContext(ctx, time.Second, false)
+	if err == nil && len(cpuPct) > 0 {
+		payload.CPUPct = round1(cpuPct[0])
+	}
+
+	vm, err := mem.VirtualMemoryWithContext(ctx)
+	if err == nil {
+		payload.MemPct = round1(vm.UsedPercent)
+	}
+
+	diskUsage, err := disk.UsageWithContext(ctx, "/")
+	if err == nil {
+		payload.DiskPct = round1(diskUsage.UsedPercent)
+	}
+
+	swapUsage, err := mem.SwapMemoryWithContext(ctx)
+	if err == nil {
+		payload.SwapPct = round1(swapUsage.UsedPercent)
+	}
+
+	avg, err := gopsload.AvgWithContext(ctx)
+	if err == nil {
+		payload.LoadAvg = []float64{round2(avg.Load1), round2(avg.Load5), round2(avg.Load15)}
+	}
+
+	hostInfo, err := host.InfoWithContext(ctx)
+	if err == nil {
+		payload.UptimeSeconds = hostInfo.Uptime
+	}
+
+	nginxInstalled, nginxSites, err := detectNginx()
+	if err != nil {
+		return payload, err
+	}
+	payload.NginxInstalled = nginxInstalled
+	payload.NginxSites = nginxSites
+
+	return payload, nil
+}
+
+func Send(ctx context.Context, client *http.Client, cfg config.Config, payload Payload) error {
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshal payload: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, strings.TrimRight(cfg.BackendURL, "/")+"/monitor/server/heartbeat-v2", strings.NewReader(string(body)))
+	if err != nil {
+		return fmt.Errorf("build request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("X-API-Key", cfg.APIKey)
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return fmt.Errorf("send request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("heartbeat failed with status %s", resp.Status)
+	}
+	return nil
+}
+
+func detectNginx() (bool, []string, error) {
+	installed := false
+	if _, err := exec.LookPath("nginx"); err == nil {
+		installed = true
+	}
+	for _, path := range []string{"/etc/nginx/nginx.conf", "/usr/local/etc/nginx/nginx.conf", "/opt/homebrew/etc/nginx/nginx.conf"} {
+		if _, err := os.Stat(path); err == nil {
+			installed = true
+			break
+		}
+	}
+	if !installed {
+		return false, []string{}, nil
+	}
+
+	dir := "/etc/nginx/sites-enabled"
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return true, []string{}, nil
+		}
+		return true, nil, fmt.Errorf("read nginx sites-enabled: %w", err)
+	}
+
+	sites := make([]string, 0, len(entries))
+	for _, entry := range entries {
+		name := entry.Name()
+		fullPath := filepath.Join(dir, name)
+		if entry.Type()&os.ModeSymlink != 0 {
+			if target, err := os.Readlink(fullPath); err == nil {
+				name = fmt.Sprintf("%s -> %s", name, target)
+			}
+		}
+		sites = append(sites, name)
+	}
+	sort.Strings(sites)
+	return true, sites, nil
+}
+
+func round1(v float64) float64 {
+	return float64(int(v*10+0.5)) / 10
+}
+
+func round2(v float64) float64 {
+	return float64(int(v*100+0.5)) / 100
+}