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/billing.go

@@ -3,7 +3,6 @@ package models
 import (
 	"time"
 
-	"gorm.io/gorm"
 )
 
 // CloudBilling 云账单模型 - 每日成本记录
@@ -21,11 +20,10 @@ type CloudBilling struct {
 	Description   string         `gorm:"size:500" json:"description"`
 	CreatedAt     time.Time      `json:"created_at"`
 	UpdatedAt     time.Time      `json:"updated_at"`
-	DeletedAt     gorm.DeletedAt `gorm:"index" json:"-"`
 }
 
 func (CloudBilling) TableName() string {
-	return "cloud_billings"
+	return "asset_cloud_billings"
 }
 
 // BillingAlertRule 账单预警规则
@@ -41,11 +39,10 @@ type BillingAlertRule struct {
 	LastTriggered *time.Time     `json:"last_triggered"`
 	CreatedAt     time.Time      `json:"created_at"`
 	UpdatedAt     time.Time      `json:"updated_at"`
-	DeletedAt     gorm.DeletedAt `gorm:"index" json:"-"`
 }
 
 func (BillingAlertRule) TableName() string {
-	return "billing_alert_rules"
+	return "monitor_billing_alert_rules"
 }
 
 // BillingStats 账单统计