feat: AI预测分析接入真实后端数据 + 修复CloudBilling文件损坏

- AIPredictiveAnalytics: 替换3组硬编码mock为实时数据驱动预测
  - 指标预测: 基于dashboard metrics时序数据(cpu/memory/disk)线性回归计算斜率与R²
  - 容量规划: 基于日均增长率推算阈值触及时间(天),动态生成AI扩容建议
  - 异常预测: 基于告警规则阈值+当前趋势+事件频率计算异常触发概率
  - 概览卡片数据驱动化(置信度基于R²拟合度,高风险/容量预警计数实时计算)
- CloudBilling.tsx: 修复read_file导致的行号前缀损坏(501行全部含N|前缀)

backend/internal/models/billing.go

@@ -0,0 +1,108 @@
+package models
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+// CloudBilling 云账单模型 - 每日成本记录
+type CloudBilling struct {
+	ID            uint           `gorm:"primarykey" json:"id"`
+	CloudAccountID *uint         `gorm:"index" json:"cloud_account_id"`
+	AccountName   string         `gorm:"size:128" json:"account_name"`
+	Provider      string         `gorm:"size:64;index" json:"provider"` // aliyun, tencent, aws, huawei, azure
+	BillingDate   string         `gorm:"size:10;index;not null" json:"billing_date"` // YYYY-MM-DD
+	Cost          float64        `gorm:"type:decimal(12,2);default:0" json:"cost"`   // 费用（元）
+	Currency      string         `gorm:"size:8;default:CNY" json:"currency"`         // CNY, USD
+	Service       string         `gorm:"size:128" json:"service"`                    // ECS, RDS, OSS, CDN 等
+	Region        string         `gorm:"size:64" json:"region"`
+	Tags          string         `gorm:"type:text" json:"tags"` // JSON
+	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"
+}
+
+// BillingAlertRule 账单预警规则
+type BillingAlertRule struct {
+	ID            uint           `gorm:"primarykey" json:"id"`
+	Name          string         `gorm:"size:128;not null" json:"name"`
+	Provider      string         `gorm:"size:64" json:"provider"`                // 空=所有云厂商
+	CloudAccountID *uint         `gorm:"index" json:"cloud_account_id"`          // 空=所有账号
+	Metric        string         `gorm:"size:32;default:daily" json:"metric"`    // daily, monthly
+	Threshold     float64        `gorm:"type:decimal(12,2)" json:"threshold"`    // 阈值（元）
+	Operator      string         `gorm:"size:8;default:>" json:"operator"`       // >, >=, <, <=
+	Enabled       bool           `gorm:"default:true" json:"enabled"`
+	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"
+}
+
+// BillingStats 账单统计
+type BillingStats struct {
+	TodayCost    float64                 `json:"today_cost"`
+	MonthCost    float64                 `json:"month_cost"`
+	YearCost     float64                 `json:"year_cost"`
+	YesterdayCost float64                `json:"yesterday_cost"`
+	MonthTrend   []DailyCost             `json:"month_trend"`
+	ProviderDist []ProviderCost          `json:"provider_dist"`
+	Alerts       []BillingAlert          `json:"alerts"`
+}
+
+// DailyCost 每日成本
+type DailyCost struct {
+	Date  string  `json:"date"`
+	Cost  float64 `json:"cost"`
+}
+
+// ProviderCost 厂商成本分布
+type ProviderCost struct {
+	Provider string  `json:"provider"`
+	Cost     float64 `json:"cost"`
+	Percent  float64 `json:"percent"`
+}
+
+// BillingAlert 账单预警
+type BillingAlert struct {
+	RuleID    uint    `json:"rule_id"`
+	RuleName  string  `json:"rule_name"`
+	Provider  string  `json:"provider"`
+	Current   float64 `json:"current"`
+	Threshold float64 `json:"threshold"`
+	Metric    string  `json:"metric"`
+	Operator  string  `json:"operator"`
+}
+
+// CreateBillingRequest 创建账单记录请求
+type CreateBillingRequest struct {
+	CloudAccountID *uint  `json:"cloud_account_id"`
+	AccountName    string `json:"account_name"`
+	Provider       string `json:"provider" binding:"required"`
+	BillingDate    string `json:"billing_date" binding:"required"`
+	Cost           float64 `json:"cost" binding:"required"`
+	Currency       string `json:"currency"`
+	Service        string `json:"service"`
+	Region         string `json:"region"`
+	Description    string `json:"description"`
+}
+
+// CreateBillingAlertRequest 创建预警规则请求
+type CreateBillingAlertRequest struct {
+	Name           string  `json:"name" binding:"required"`
+	Provider       string  `json:"provider"`
+	CloudAccountID *uint   `json:"cloud_account_id"`
+	Metric         string  `json:"metric"`
+	Threshold      float64 `json:"threshold" binding:"required"`
+	Operator       string  `json:"operator"`
+	Enabled        bool    `json:"enabled"`
+}