docs: update README, API reference, dev-log, project structure with Agent monitoring + quick-alarm + latest fixes

- README.md: React 19, default pwd 123456, Docker Compose deploy, correct module list
- api-reference.md: add Agent monitoring section (report/latest/rules/quick-setup/alerts/tasks/kline)
- dev-log.md: new entry documenting hostname/IP fix, system collector, offline detection, quick alarm
- project-structure.md: add agent/ directory, dev-log.md link, React 19

backend/internal/api/handlers/agent_task.go

@@ -152,6 +152,82 @@ func (h *AgentTaskHandler) GetTask(c *gin.Context) {
 
 // ===== Agent 告警规则 =====
 
+// QuickSetupRules POST /api/v1/agent/rules/quick-setup
+// 一键创建默认告警规则（CPU/内存/磁盘/网络带宽），作用于所有在线主机
+func (h *AgentTaskHandler) QuickSetupRules(c *gin.Context) {
+	var req struct {
+		Type string `json:"type"` // "ecs" 或留空
+	}
+	c.ShouldBindJSON(&req)
+
+	// 获取所有在线主机
+	var onlineHosts []string
+	h.db.Model(&models.Server{}).
+		Where("agent_status = ?", "online").
+		Pluck("hostname", &onlineHosts)
+
+	if len(onlineHosts) == 0 {
+		// 如果没有在线主机，尝试从 agent_reports 中获取最近 3 分钟活跃的主机名
+		h.db.Model(&models.AgentReport{}).
+			Where("report_time >= ?", time.Now().Add(-3*time.Minute)).
+			Distinct("hostname").
+			Pluck("hostname", &onlineHosts)
+	}
+
+	if len(onlineHosts) == 0 {
+		c.JSON(400, models.Response{Code: 400, Message: "没有在线的主机，请先安装并启动 Agent"})
+		return
+	}
+
+	type ruleDef struct {
+		Name     string
+		Metric   string
+		Operator string
+		Threshold float64
+		Duration int
+	}
+
+	defaultRules := []ruleDef{
+		{Name: "CPU使用率(Warn)", Metric: "cpu", Operator: ">", Threshold: 80},
+		{Name: "内存使用率(Warn)", Metric: "mem", Operator: ">", Threshold: 80},
+		{Name: "磁盘使用率(Warn)", Metric: "disk", Operator: ">", Threshold: 80},
+		{Name: "网络带宽使用率(Warn)", Metric: "net", Operator: ">", Threshold: 80},
+	}
+
+	created := 0
+	skipped := 0
+	for _, host := range onlineHosts {
+		for _, def := range defaultRules {
+			// 检查是否已存在同名同主机的规则，避免重复创建
+			var existing models.AgentRule
+			h.db.Where("name = ? AND hostname = ?", def.Name, host).First(&existing)
+			if existing.ID > 0 {
+				skipped++
+				continue
+			}
+
+			rule := models.AgentRule{
+				Name:      def.Name,
+				Hostname:  host,
+				Metric:    def.Metric,
+				Operator:  def.Operator,
+				Threshold: def.Threshold,
+				Enabled:   true,
+			}
+			if err := h.db.Create(&rule).Error; err != nil {
+				continue
+			}
+			created++
+		}
+	}
+
+	c.JSON(200, models.Response{
+		Code:    200,
+		Message: fmt.Sprintf("已为 %d 台主机创建 %d 条规则（跳过 %d 条已存在的)", len(onlineHosts), created, skipped),
+		Data:    gin.H{"hosts": len(onlineHosts), "created": created, "skipped": skipped},
+	})
+}
+
 // ListRules GET /api/v1/agent/rules
 func (h *AgentTaskHandler) ListRules(c *gin.Context) {
 	var rules []models.AgentRule