💥 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/config/config_test.go

@@ -0,0 +1,71 @@
+package config
+
+import (
+	"os"
+	"testing"
+	"time"
+)
+
+// TestDefaultConfigUsesLocalhostAndSaneIntervals verifies safe local defaults.
+func TestDefaultConfigUsesLocalhostAndSaneIntervals(t *testing.T) {
+	cfg := Default()
+
+	if cfg.HTTP.ListenAddress != "127.0.0.1:8080" {
+		t.Fatalf("listen address = %q", cfg.HTTP.ListenAddress)
+	}
+	if cfg.Collect.Interval <= 0 || cfg.Collect.Timeout <= 0 {
+		t.Fatalf("collect intervals must be positive: %+v", cfg.Collect)
+	}
+	if cfg.Report.Enabled {
+		t.Fatal("reporting should be disabled by default")
+	}
+}
+
+// TestLoadAppliesEnvironmentOverrides verifies environment variables override defaults.
+func TestLoadAppliesEnvironmentOverrides(t *testing.T) {
+	t.Setenv("MFD_AGENT_LISTEN", "127.0.0.1:9090")
+	t.Setenv("MFD_AGENT_REPORT_ENABLED", "true")
+	t.Setenv("MFD_AGENT_REPORT_ENDPOINT", "http://center/status")
+	t.Setenv("MFD_AGENT_REPORT_INTERVAL", "2s")
+	t.Setenv("MFD_AGENT_HOST_ID", "host-a")
+
+	cfg, err := Load("")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if cfg.HTTP.ListenAddress != "127.0.0.1:9090" {
+		t.Fatalf("listen address = %q", cfg.HTTP.ListenAddress)
+	}
+	if !cfg.Report.Enabled || cfg.Report.Endpoint != "http://center/status" {
+		t.Fatalf("report config not applied: %+v", cfg.Report)
+	}
+	if cfg.Report.Interval.Duration() != 2*time.Second {
+		t.Fatalf("report interval = %s", cfg.Report.Interval.Duration())
+	}
+	if cfg.HostID != "host-a" {
+		t.Fatalf("host id = %q", cfg.HostID)
+	}
+}
+
+// TestLoadJSONConfigFile verifies JSON config files are parsed into Config.
+func TestLoadJSONConfigFile(t *testing.T) {
+	file, err := os.CreateTemp(t.TempDir(), "config-*.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, _ = file.WriteString(`{"http":{"listen_address":"127.0.0.1:7070"},"collect":{"interval":"3s","timeout":"1s"}}`)
+	_ = file.Close()
+
+	cfg, err := Load(file.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if cfg.HTTP.ListenAddress != "127.0.0.1:7070" {
+		t.Fatalf("listen address = %q", cfg.HTTP.ListenAddress)
+	}
+	if cfg.Collect.Interval.Duration() != 3*time.Second || cfg.Collect.Timeout.Duration() != time.Second {
+		t.Fatalf("collect config = %+v", cfg.Collect)
+	}
+}