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/api/routes/routes.go

@@ -371,24 +371,6 @@ func Register(r *gin.Engine, db *gorm.DB, log *zap.Logger, cfg *config.Config) {
 		audit.POST("/logs/clear", auditHandler.ClearAuditLogs)
 	}
 
-	// SQL审计路由 // Logan.Li
-	sqlAuditHandler := handlers.NewSQLAuditHandler(db)
-	sqlAudit := authorized.Group("/sql-audit")
-	{
-		sqlAudit.GET("/records", sqlAuditHandler.ListRecords)
-		sqlAudit.GET("/records/:id", sqlAuditHandler.GetRecord)
-		sqlAudit.POST("/analyze", sqlAuditHandler.AnalyzeSQL)
-		sqlAudit.POST("/records/:id/approve", sqlAuditHandler.ApproveRecord)
-		sqlAudit.POST("/records/:id/reject", sqlAuditHandler.RejectRecord)
-		sqlAudit.POST("/records/:id/execute", sqlAuditHandler.ExecuteRecord)
-		sqlAudit.DELETE("/records/:id", sqlAuditHandler.DeleteRecord)
-		sqlAudit.GET("/rules", sqlAuditHandler.ListRules)
-		sqlAudit.POST("/rules", sqlAuditHandler.CreateRule)
-		sqlAudit.PUT("/rules/:id", sqlAuditHandler.UpdateRule)
-		sqlAudit.DELETE("/rules/:id", sqlAuditHandler.DeleteRule)
-		sqlAudit.POST("/rules/:id/toggle", sqlAuditHandler.ToggleRule)
-	}
-
 	// Agent 上报路由（无需 JWT）
 	agentHandler := handlers.NewAgentHandler(db)
 	taskHandler := handlers.NewAgentTaskHandler(db)