feat: add server log file management to performance settings

Add API endpoints (GET/DELETE /api/performance/logs) to list and clean up
server log files by count or by age. Track the active log file path in
the logger to prevent deleting the currently open log. Add a management
UI section in the performance settings page with log directory info,
file statistics, and cleanup controls. Includes i18n translations for
all supported languages (en, fr, ja, ru, vi, zh-CN, zh-TW).

router/api-router.go

@@ -194,6 +194,8 @@ func SetApiRouter(router *gin.Engine) {
 			performanceRoute.DELETE("/disk_cache", controller.ClearDiskCache)
 			performanceRoute.POST("/reset_stats", controller.ResetPerformanceStats)
 			performanceRoute.POST("/gc", controller.ForceGC)
+			performanceRoute.GET("/logs", controller.GetLogFiles)
+			performanceRoute.DELETE("/logs", controller.CleanupLogFiles)
 		}
 		ratioSyncRoute := apiRouter.Group("/ratio_sync")
 		ratioSyncRoute.Use(middleware.RootAuth())