feat(dashboard): more System History metrics, persistence & localized labels

- Sample swap %, TCP/UDP connection counts and disk-usage % on the host ticker
- System History: Swap overlaid on the RAM tab, plus new Connections and Disk Usage tabs
- Persist the host time-series across restarts: gob snapshot beside the DB, written on a timer and at shutdown, restored on boot
- Live-refresh the open chart (2s for short ranges, 10s for longer)
- Localize CPU/RAM/Swap and the new tab/chart titles across all 13 languages and route legend series names through i18n

web/controller/server.go

@@ -33,6 +33,7 @@ type ServerController struct {
 // NewServerController creates a new ServerController, initializes routes, and starts background tasks.
 func NewServerController(g *gin.RouterGroup) *ServerController {
 	a := &ServerController{}
+	service.RestoreSystemMetrics()
 	a.initRouter(g)
 	a.startTask()
 	return a
@@ -84,6 +85,11 @@ func (a *ServerController) startTask() {
 		a.xrayMetricsService.Sample(time.Now())
 		websocket.BroadcastStatus(status)
 	})
+	c.AddFunc("@every 1m", func() {
+		if err := service.PersistSystemMetrics(); err != nil {
+			logger.Warning("persist system metrics failed:", err)
+		}
+	})
 }
 
 // status returns the current server status information.