feat(audit): F1+F2 告警静默规则标记完成 + 审计日志CSV导出实现

F1 告警静默规则 [done]:
- 后端 alert_silence.go: CRUD + Toggle (onetime/daily/weekly 三模式)
- 告警引擎 isSilenced 集成 (alert_engine.go)
- 前端 SilenceRuleTab + SilenceDialog
- 路由 /alerts/silences 已注册

F2 审计日志导出 [done]:
- 重写 ExportAuditLogs: 真正的 CSV 导出 (encoding/csv + UTF-8 BOM)
- 支持 module/action/username/startTime/endTime 筛选
- 导出限制 10000 条防溢出，自动记录审计日志
- JSON 格式向后兼容 (format=json)
- 前端 exportLogs 传递查询参数

同时包含累积的前期工作:
- 目录重构 internal/ -> controller/model/router (v0.55-v0.57)
- 后端分层架构 dto/repository/service/utils
- 审计模块全功能 (终端审计/操作审计/登录日志)
- asciicast v2 录制格式
- SFTP 文件浏览器
- StatStrip 紧凑统计条
- 在线会话自动刷新
- LiveMonitor WebSocket 诊断修复

验证: go build ✅ | npm run build ✅ | Docker 部署 ✅ | 10 回归端点 ✅ | CSV 导出 ✅ | 静默 CRUD ✅

backend/model/approval.go

@@ -0,0 +1,107 @@
+package model
+
+import (
+	"time"
+
+)
+
+// ApprovalTemplate 审批模板模型
+type ApprovalTemplate struct {
+	ID          uint           `gorm:"primarykey" json:"id"`
+	Name        string         `gorm:"size:128;not null" json:"name"`
+	Code        string         `gorm:"size:64;uniqueIndex;not null" json:"code"`
+	Description string         `gorm:"size:500" json:"description"`
+	Type        string         `gorm:"size:32;not null" json:"type"` // release, server_apply, app_deploy, permission_request
+	FormSchema  string         `gorm:"type:text" json:"form_schema"` // JSON form fields config
+	FlowConfig  string         `gorm:"type:text" json:"flow_config"` // JSON approval flow steps
+	Category    string         `gorm:"size:32;default:resource" json:"category"` // resource, app, permission
+	Enabled     bool           `gorm:"default:true" json:"enabled"`
+	CreatedAt   time.Time      `json:"created_at"`
+	UpdatedAt   time.Time      `json:"updated_at"`
+}
+
+// TableName 表名
+func (ApprovalTemplate) TableName() string {
+	return "sys_approval_templates"
+}
+
+// ApprovalProcess 审批流程模型
+type ApprovalProcess struct {
+	ID         uint           `gorm:"primarykey" json:"id"`
+	TemplateID uint           `json:"template_id"`
+	Title      string         `gorm:"size:255;not null" json:"title"`
+	Applicant  uint           `json:"applicant"`
+	Status     string         `gorm:"size:32;default:pending" json:"status"` // pending, approved, rejected
+	FormData   string         `gorm:"type:text" json:"form_data"` // JSON
+	CurrentStep int           `gorm:"default:0" json:"current_step"`
+	TotalSteps  int           `json:"total_steps"`
+	ApprovedAt *time.Time     `json:"approved_at"`
+	RejectedAt *time.Time     `json:"rejected_at"`
+	RejectReason string       `gorm:"size:500" json:"reject_reason"`
+	CreatedAt  time.Time      `json:"created_at"`
+	UpdatedAt  time.Time      `json:"updated_at"`
+
+	// 关联
+	Template      *ApprovalTemplate `gorm:"foreignKey:TemplateID" json:"template,omitempty"`
+	ApplicantUser *User             `gorm:"foreignKey:Applicant" json:"applicant_user,omitempty"`
+	Steps         []ApprovalStep    `gorm:"foreignKey:ProcessID" json:"steps,omitempty"`
+}
+
+// TableName 表名
+func (ApprovalProcess) TableName() string {
+	return "approval_processes"
+}
+
+// ApprovalStep 审批步骤模型
+type ApprovalStep struct {
+	ID        uint           `gorm:"primarykey" json:"id"`
+	ProcessID uint           `json:"process_id"`
+	Step      int            `json:"step"`
+	Approver  uint           `json:"approver"`
+	Status    string         `gorm:"size:32;default:pending" json:"status"` // pending, approved, rejected
+	Comment   string         `gorm:"size:500" json:"comment"`
+	ApprovedAt *time.Time    `json:"approved_at"`
+	CreatedAt time.Time      `json:"created_at"`
+	UpdatedAt time.Time      `json:"updated_at"`
+
+	// 关联
+	ApproverUser *User `gorm:"foreignKey:Approver" json:"approver_user,omitempty"`
+}
+
+// TableName 表名
+func (ApprovalStep) TableName() string {
+	return "approval_steps"
+}
+
+// CreateApprovalTemplateRequest 创建审批模板请求
+type CreateApprovalTemplateRequest struct {
+	Name        string `json:"name" binding:"required"`
+	Code        string `json:"code" binding:"required"`
+	Description string `json:"description"`
+	Type        string `json:"type" binding:"required,oneof=server_apply app_deploy permission_request"`
+	Category    string `json:"category"` // resource, app, permission
+	FormSchema  string `json:"form_schema"`
+	FlowConfig  string `json:"flow_config"`
+}
+
+// CreateApprovalProcessRequest 创建审批流程请求
+type CreateApprovalProcessRequest struct {
+	TemplateID uint   `json:"template_id" binding:"required"`
+	Title      string `json:"title" binding:"required"`
+	FormData   string `json:"form_data"`
+}
+
+// ApproveRequest 审批请求
+type ApproveRequest struct {
+	Status string `json:"status"`
+	Comment string `json:"comment"`
+}
+
+// ApprovalStats 审批统计
+type ApprovalStats struct {
+	Pending  int64 `json:"pending"`
+	Approved int64 `json:"approved"`
+	Rejected int64 `json:"rejected"`
+	Total    int64 `json:"total"`
+	MyPending int64 `json:"my_pending"`
+}