refactor: 清理SQL审计全栈死代码 (删除孤立组件+handler+model+路由+mock+API定义, 共-1278行)

SQL审计菜单此前已从侧边栏移除，但死代码残留(违反step5清理清单):
- 删除 frontend/components/audit/SQLAuditManager.tsx (629行, 无任何外部引用)
- 删除 backend/handlers/sql_audit.go (435行) + backend/models/sql_audit.go (64行)
- 移除 routes.go 中13条SQL审计路由 (API不再暴露, 返回404)
- 移除 database.go AutoMigrate 中2个SQL审计表
- 移除 api.ts sqlAuditApi 对象 (37行)
- 移除 mocks SQL审计mock数据 (90行) + barrel引用

backend/internal/models/sql_audit.go

@@ -1,64 +0,0 @@
-package models
-
-import (
-	"time"
-
-	"gorm.io/gorm"
-)
-
-// SQLAuditRecord SQL审计记录 // Logan.Li
-type SQLAuditRecord struct {
-	ID            uint           `gorm:"primarykey" json:"id"`
-	SQLContent    string         `gorm:"type:text;not null" json:"sql_content"`
-	SQLType       string         `gorm:"size:50" json:"sql_type"`        // DDL/DML/DQL/DCL
-	DatabaseName  string         `gorm:"size:255" json:"database_name"`
-	TargetTable   string         `gorm:"column:table_name;size:255" json:"table_name"`
-	RiskLevel     string         `gorm:"size:20;default:safe" json:"risk_level"` // high/medium/low/safe
-	RiskRules     string         `gorm:"type:text" json:"risk_rules"`            // JSON 数组
-	Status        string         `gorm:"size:20;default:pending" json:"status"`  // pending/approved/rejected/executed
-	Executor      string         `gorm:"size:255" json:"executor"`
-	Approver      string         `gorm:"size:255" json:"approver"`
-	ExecuteTime   *time.Time     `json:"execute_time"`
-	AffectedRows  int64          `gorm:"default:0" json:"affected_rows"`
-	ExecutionTime int64          `gorm:"default:0" json:"execution_time"` // 毫秒
-	SourceIP      string         `gorm:"size:100" json:"source_ip"`
-	Application   string         `gorm:"size:255" json:"application"`
-	TicketID      string         `gorm:"size:100" json:"ticket_id"`
-	CreatedAt     time.Time      `json:"created_at"`
-	UpdatedAt     time.Time      `json:"updated_at"`
-	DeletedAt     gorm.DeletedAt `gorm:"index" json:"-"`
-}
-
-func (SQLAuditRecord) TableName() string { return "sql_audit_records" }
-
-// SQLAuditRule SQL审计规则 // Logan.Li
-type SQLAuditRule struct {
-	ID          uint           `gorm:"primarykey" json:"id"`
-	Name        string         `gorm:"size:255;not null" json:"name"`
-	Description string         `gorm:"type:text" json:"description"`
-	Pattern     string         `gorm:"type:text" json:"pattern"` // 正则/关键词匹配
-	Enabled     bool           `gorm:"default:true" json:"enabled"`
-	Severity    string         `gorm:"size:20;default:medium" json:"severity"` // high/medium/low
-	Category    string         `gorm:"size:100" json:"category"`              // DDL/DML/DROP/TRUNCATE/etc
-	CreatedAt   time.Time      `json:"created_at"`
-	UpdatedAt   time.Time      `json:"updated_at"`
-	DeletedAt   gorm.DeletedAt `gorm:"index" json:"-"`
-}
-
-func (SQLAuditRule) TableName() string { return "sql_audit_rules" }
-
-// AnalyzeSQLRequest SQL分析请求 // Logan.Li
-type AnalyzeSQLRequest struct {
-	SQL           string `json:"sql"`
-	DatabaseName  string `json:"database_name"`
-	Application   string `json:"application"`
-}
-
-// AnalyzeSQLResponse SQL分析响应 // Logan.Li
-type AnalyzeSQLResponse struct {
-	ID         int64    `json:"id"`
-	RiskLevel  string   `json:"risk_level"`
-	RiskRules  []string `json:"risk_rules"`
-	SQLType    string   `json:"sql_type"`
-	TableName  string   `json:"table_name"`
-}