fix: correct telemetry identifier and visibility when containerized

Three related fixes for running Monitor inside a container with
/:/host:ro bind-mounted and network_mode: host.

* config: when HF_MONITER_ROOTFS is set, read the default identifier
  from <rootFS>/etc/hostname instead of os.Hostname(). Under
  network_mode: host the UTS namespace is not shared, so os.Hostname()
  returns a random docker-assigned string that changes across
  recreations, causing the backend to treat each restart as a new
  server.

* telemetry: log gopsutil errors from BuildPayload instead of silently
  swallowing them. Previously a missing /host mount would send a
  payload full of zeroed fields with no indication of failure.

* docker-compose: drop the 'ports:' block. It is silently ignored
  under network_mode: host (the bridge server binds directly on the
  host's 127.0.0.1:MONITOR_PORT).

internal/telemetry/telemetry.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"log"
 	"net/http"
 	"os"
 	"os/exec"
@@ -50,12 +51,15 @@ func BuildPayload(ctx context.Context, cfg config.Config) (Payload, error) {
 	}
 
 	cpuPct, err := cpu.PercentWithContext(ctx, time.Second, false)
-	if err == nil && len(cpuPct) > 0 {
+	if err != nil {
+		log.Printf("telemetry: cpu.Percent failed: %v", err)
+	} else if len(cpuPct) > 0 {
 		payload.CPUPct = round1(cpuPct[0])
 	}
 
-	vm, err := mem.VirtualMemoryWithContext(ctx)
-	if err == nil {
+	if vm, err := mem.VirtualMemoryWithContext(ctx); err != nil {
+		log.Printf("telemetry: mem.VirtualMemory failed: %v", err)
+	} else {
 		payload.MemPct = round1(vm.UsedPercent)
 	}
 
@@ -63,28 +67,33 @@ func BuildPayload(ctx context.Context, cfg config.Config) (Payload, error) {
 	if diskPath == "" {
 		diskPath = "/"
 	}
-	diskUsage, err := disk.UsageWithContext(ctx, diskPath)
-	if err == nil {
+	if diskUsage, err := disk.UsageWithContext(ctx, diskPath); err != nil {
+		log.Printf("telemetry: disk.Usage(%s) failed: %v", diskPath, err)
+	} else {
 		payload.DiskPct = round1(diskUsage.UsedPercent)
 	}
 
-	swapUsage, err := mem.SwapMemoryWithContext(ctx)
-	if err == nil {
+	if swapUsage, err := mem.SwapMemoryWithContext(ctx); err != nil {
+		log.Printf("telemetry: mem.SwapMemory failed: %v", err)
+	} else {
 		payload.SwapPct = round1(swapUsage.UsedPercent)
 	}
 
-	avg, err := gopsload.AvgWithContext(ctx)
-	if err == nil {
+	if avg, err := gopsload.AvgWithContext(ctx); err != nil {
+		log.Printf("telemetry: load.Avg failed: %v", err)
+	} else {
 		payload.LoadAvg = []float64{round2(avg.Load1), round2(avg.Load5), round2(avg.Load15)}
 	}
 
-	hostInfo, err := host.InfoWithContext(ctx)
-	if err == nil {
+	if hostInfo, err := host.InfoWithContext(ctx); err != nil {
+		log.Printf("telemetry: host.Info failed: %v", err)
+	} else {
 		payload.UptimeSeconds = hostInfo.Uptime
 	}
 
-	nginxInstalled, nginxSites, err := detectNginx(cfg.RootFS)
-	if err == nil {
+	if nginxInstalled, nginxSites, err := detectNginx(cfg.RootFS); err != nil {
+		log.Printf("telemetry: detectNginx failed: %v", err)
+	} else {
 		payload.NginxInstalled = nginxInstalled
 		payload.NginxSites = nginxSites
 	}