P7: restore agent node type, agent heartbeat expiry, build-version injection, remove log/history/xray-metrics modules, optional sub port

- nodes: port node-type (traditional/agent) picker back from web-src into
  the embedded frontend; backend annotates NodeView.nodeType from
  agent_nodes bindings; fix agent-node update path (skip reachability
  probe and apiToken requirement for agent-managed nodes); restore i18n
  keys in all 13 locales; install command now uses the Gitea mirror
- jobs: expire agent-bound nodes whose agent_nodes.last_seen is older
  than max(3x heartbeat interval, 120s) = 180s; last_seen=0 (never
  registered) is left untouched; transitions reuse UpdateHeartbeat +
  node event broadcast
- config: GetBaseVersion honors ldflags-injected buildVersion; release
  builds inject 3.7.0-agent.1 so the panel no longer reports a phantom
  update against the Gitea release tag
- logger/server: remove the three log viewers (panel/xray/amneziawg),
  their API endpoints and the 10240-entry in-memory log buffer; file
  logging via lumberjack unchanged; tests assert via a new optional
  logger hook instead of the removed buffer
- server: remove system history and xray metrics modules end to end
  (endpoints, sampling appends in RefreshStatus, per-minute persist
  cron, gob snapshot/restore, XrayMetricsService); realtime status and
  per-node history are untouched
- settings: subPort may be 0/unset - subscription links are generated
  without a port while the subscription service keeps binding the
  default 2096; the settings form declares the cleared state via
  onNumber's new onClear option instead of snapping back to 1

internal/web/web.go

@@ -491,7 +491,6 @@ func (s *Server) start(restartXray bool) (err error) {
 
 	// Create event bus before startTask so jobs can use it
 	s.bus = eventbus.New(eventbus.DefaultBufferSize)
-	service.SetEventBus(s.bus)
 	job.EventBus = s.bus
 
 	// Wire xray crash callback BEFORE startTask so it's ready
@@ -531,9 +530,6 @@ func (s *Server) stop(stopXray bool) error {
 	if s.bus != nil {
 		s.bus.Stop()
 	}
-	if err := service.PersistSystemMetrics(); err != nil {
-		logger.Warning("persist system metrics on shutdown failed:", err)
-	}
 	if stopXray {
 		service.StopTrafficWriter()
 	}