💥 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.go

@@ -0,0 +1,149 @@
+package config
+
+import (
+	"encoding/json"
+	"errors"
+	"os"
+	"strconv"
+	"time"
+)
+
+// Config contains all runtime, reporting, collection, and service settings.
+type Config struct {
+	HostID  string        `json:"host_id"`
+	HTTP    HTTPConfig    `json:"http"`
+	Collect CollectConfig `json:"collect"`
+	Report  ReportConfig  `json:"report"`
+	Service ServiceConfig `json:"service"`
+}
+
+// HTTPConfig controls the local HTTP API listener.
+type HTTPConfig struct {
+	ListenAddress string `json:"listen_address"`
+}
+
+// CollectConfig controls periodic host status collection.
+type CollectConfig struct {
+	Interval Duration `json:"interval"`
+	Timeout  Duration `json:"timeout"`
+}
+
+// ReportConfig controls optional periodic status POST reporting.
+type ReportConfig struct {
+	Enabled  bool     `json:"enabled"`
+	Endpoint string   `json:"endpoint"`
+	Interval Duration `json:"interval"`
+	Timeout  Duration `json:"timeout"`
+}
+
+// ServiceConfig controls operating system service registration metadata.
+type ServiceConfig struct {
+	Name        string `json:"name"`
+	DisplayName string `json:"display_name"`
+	Description string `json:"description"`
+}
+
+// Duration wraps time.Duration so JSON config can use Go duration strings.
+type Duration time.Duration
+
+// Duration returns the standard library duration value.
+func (d Duration) Duration() time.Duration {
+	return time.Duration(d)
+}
+
+// MarshalJSON writes the duration as a Go duration string such as "30s".
+func (d Duration) MarshalJSON() ([]byte, error) {
+	return json.Marshal(time.Duration(d).String())
+}
+
+// UnmarshalJSON parses a Go duration string from JSON.
+func (d *Duration) UnmarshalJSON(data []byte) error {
+	var raw string
+	if err := json.Unmarshal(data, &raw); err != nil {
+		return err
+	}
+	parsed, err := time.ParseDuration(raw)
+	if err != nil {
+		return err
+	}
+	*d = Duration(parsed)
+	return nil
+}
+
+// Default returns safe local defaults for running the agent.
+func Default() Config {
+	return Config{
+		HTTP: HTTPConfig{ListenAddress: "127.0.0.1:8080"},
+		Collect: CollectConfig{
+			Interval: Duration(30 * time.Second),
+			Timeout:  Duration(10 * time.Second),
+		},
+		Report: ReportConfig{
+			Enabled:  false,
+			Interval: Duration(60 * time.Second),
+			Timeout:  Duration(5 * time.Second),
+		},
+		Service: ServiceConfig{
+			Name:        "mfd-monitor-agent",
+			DisplayName: "MFD Monitor Agent",
+			Description: "Collects host status and exposes it over HTTP.",
+		},
+	}
+}
+
+// Load reads optional JSON config, applies environment overrides, and validates required settings.
+func Load(path string) (Config, error) {
+	cfg := Default()
+	if path != "" {
+		data, err := os.ReadFile(path)
+		if err != nil {
+			return cfg, err
+		}
+		if err := json.Unmarshal(data, &cfg); err != nil {
+			return cfg, err
+		}
+	}
+	applyEnv(&cfg)
+	if cfg.Report.Enabled && cfg.Report.Endpoint == "" {
+		return cfg, errors.New("report endpoint is required when reporting is enabled")
+	}
+	return cfg, nil
+}
+
+// applyEnv overlays supported MFD_AGENT_* environment variables onto cfg.
+func applyEnv(cfg *Config) {
+	if value := os.Getenv("MFD_AGENT_HOST_ID"); value != "" {
+		cfg.HostID = value
+	}
+	if value := os.Getenv("MFD_AGENT_LISTEN"); value != "" {
+		cfg.HTTP.ListenAddress = value
+	}
+	if value := os.Getenv("MFD_AGENT_REPORT_ENABLED"); value != "" {
+		if parsed, err := strconv.ParseBool(value); err == nil {
+			cfg.Report.Enabled = parsed
+		}
+	}
+	if value := os.Getenv("MFD_AGENT_REPORT_ENDPOINT"); value != "" {
+		cfg.Report.Endpoint = value
+	}
+	if value := os.Getenv("MFD_AGENT_REPORT_INTERVAL"); value != "" {
+		if parsed, err := time.ParseDuration(value); err == nil {
+			cfg.Report.Interval = Duration(parsed)
+		}
+	}
+	if value := os.Getenv("MFD_AGENT_REPORT_TIMEOUT"); value != "" {
+		if parsed, err := time.ParseDuration(value); err == nil {
+			cfg.Report.Timeout = Duration(parsed)
+		}
+	}
+	if value := os.Getenv("MFD_AGENT_COLLECT_INTERVAL"); value != "" {
+		if parsed, err := time.ParseDuration(value); err == nil {
+			cfg.Collect.Interval = Duration(parsed)
+		}
+	}
+	if value := os.Getenv("MFD_AGENT_COLLECT_TIMEOUT"); value != "" {
+		if parsed, err := time.ParseDuration(value); err == nil {
+			cfg.Collect.Timeout = Duration(parsed)
+		}
+	}
+}