💥 feat(agent)!: 添加主机监控代理首版

* 实现周期采集、快照缓存、本地 HTTP API 和主动上报

* 补齐 Linux 和 Windows 主机、网络、资源、进程和 TCP 采集

* 添加服务生命周期管理、配置加载、构建脚本和测试覆盖

BREAKING CHANGE: network.ips 拆分为 network.ipv4s 和 network.ipv6s。

internal/service/service_linux_test.go

@@ -0,0 +1,37 @@
+//go:build linux
+
+package service
+
+import (
+	"strings"
+	"testing"
+
+	"mfd-monitor-agent/internal/config"
+)
+
+// TestRenderSystemdUnitIncludesConfigPath verifies install preserves the config flag.
+func TestRenderSystemdUnitIncludesConfigPath(t *testing.T) {
+	cfg := config.Default()
+	cfg.Service.Description = "MFD Agent"
+
+	unit := renderSystemdUnit("/opt/agent", "/etc/mfd-agent.json", cfg)
+
+	if !strings.Contains(unit, "ExecStart=/opt/agent run -config /etc/mfd-agent.json") {
+		t.Fatalf("unit missing config path:\n%s", unit)
+	}
+}
+
+// TestLinuxInstallRequiresRoot verifies Linux install rejects non-root callers.
+func TestLinuxInstallRequiresRoot(t *testing.T) {
+	oldUID := currentUID
+	t.Cleanup(func() { currentUID = oldUID })
+	currentUID = func() int { return 1000 }
+
+	err := linuxManager{}.Install("/opt/agent", config.Default(), InstallOptions{})
+	if err == nil {
+		t.Fatal("expected root requirement error")
+	}
+	if !strings.Contains(err.Error(), "root") {
+		t.Fatalf("error = %v", err)
+	}
+}