feat: Agent采集uptime, 后端持久化kernel/uptime/diskIO, 前端磁盘BPS+IOPS展示

- Agent: system.go 添加 readUptime(), SystemStat 携带 Uptime
- Backend: Server 模型新增 Kernel 字段, ReceiveReport 持久化 kernel+uptime
- Backend: /agent/latest 返回 kernel/uptime/port_info/disk_io_info/disk_total
- Frontend: 磁盘监控改为 BPS+IOPS (4张卡片), 系统信息修复内核/运行时长/监听端口/磁盘容量
- 图表单位从 MB/s 改为 KB/s, 添加 formatBPS 工具函数

backend/internal/models/metrics_aggregate.go

@@ -0,0 +1,38 @@
+package models
+
+import "time"
+
+// MetricsAggregate 指标聚合数据（Redis 热数据 → MySQL 时序聚合）// Logan.Li
+// 替代旧名 MetricsKline，OHLC 对监控无意义，改用 max/min/avg/p95
+type MetricsAggregate struct {
+	ID         uint      `gorm:"primarykey" json:"id"`
+	Hostname   string    `gorm:"size:255;index:idx_agg;not null" json:"hostname"`
+	Metric     string    `gorm:"size:32;index:idx_agg;not null" json:"metric"`     // cpu / mem / load1 / disk / net_rx / net_tx
+	Interval   string    `gorm:"size:8;index:idx_agg;not null" json:"interval"`     // 1m / 5m / 1h / 6h / 1d
+	Avg        float64   `gorm:"type:decimal(10,2)" json:"avg"`
+	MaxV       float64   `gorm:"column:max_v;type:decimal(10,2)" json:"max"`
+	MinV       float64   `gorm:"column:min_v;type:decimal(10,2)" json:"min"`
+	P95        float64   `gorm:"type:decimal(10,2)" json:"p95"`
+	Count      int       `json:"count"`
+	BucketTime time.Time `gorm:"index:idx_agg;not null" json:"bucket_time"`
+	CreatedAt  time.Time `json:"created_at"`
+}
+
+func (MetricsAggregate) TableName() string {
+	return "monitor_metrics_aggregate"
+}
+
+// AggregateReq 聚合触发请求
+type AggregateReq struct {
+	Hostname string `json:"hostname" binding:"required"`
+	Metric   string `json:"metric" binding:"required"` // cpu / mem / load1
+}
+
+// AggregateQueryReq 聚合查询参数
+type AggregateQueryReq struct {
+	Hostname string `form:"hostname" binding:"required"`
+	Metric   string `form:"metric" binding:"required"`
+	Interval string `form:"interval" binding:"required"`
+	From     string `form:"from" binding:"required"` // RFC3339
+	To       string `form:"to" binding:"required"`   // RFC3339
+}