i18n: localize sidebar theme toggle, xray-status badge, and nodes menu

The sidebar theme submenu (Theme / Dark / Ultra dark) and the dashboard's
Xray status badge ("Xray is running" etc.) were hardcoded English strings.
Wire them through vue-i18n: ThemeSwitch.vue uses menu.theme/dark/ultraDark,
and XrayStatusCard.vue derives the badge text from the existing
pages.index.xrayStatus{Running,Stop,Error,Unknown} keys (status.js no
longer carries an English stateMsg field).

The "Nodes" menu item was already keyed as menu.nodes but only en-US and
fa-IR had a translation; add it to the other 11 languages, matching the
wording each file already uses for pages.nodes.title.
#4201

web/web.go

@@ -280,8 +280,7 @@ func (s *Server) startTask() {
 
 	go func() {
 		time.Sleep(time.Second * 5)
-		// Statistics every 10 seconds, start the delay for 5 seconds for the first time, and staggered with the time to restart xray
-		s.cron.AddJob("@every 10s", job.NewXrayTrafficJob())
+		s.cron.AddJob("@every 5s", job.NewXrayTrafficJob())
 	}()
 
 	// check client ips from log file every 10 sec