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/models/agent.go

@@ -54,6 +54,7 @@ type AgentLatestResponse struct {
 // AgentReportRequest Agent 上报请求体 // Logan.Li
 type AgentReportRequest struct {
 	Hostname     string       `json:"hostname" binding:"required"`
+	IP           string       `json:"ip"`       // Agent 探测的本机 IP
 	Timestamp    string       `json:"timestamp"`
 	AgentVersion string       `json:"agent_version"` // Agent 版本号
 	CPU          CPUMetric    `json:"cpu"`
@@ -62,6 +63,13 @@ type AgentReportRequest struct {
 	Ports        []PortMetric `json:"ports"`
 	Network      NetworkStat  `json:"network"`  // 网络指标
 	DiskIO       DiskIOStat   `json:"disk_io"`  // 磁盘 IO
+	System       *SystemStat  `json:"system,omitempty"` // 系统信息（首次/变更时上报）
+}
+
+// SystemStat 系统静态信息（OS/内核等）// Logan.Li
+type SystemStat struct {
+	OSVersion string `json:"os_version"` // OS 版本 (如 "Ubuntu 22.04")
+	Kernel    string `json:"kernel"`     // 内核版本
 }
 
 type CPUMetric struct {