feat: add controller self-update mechanism (v0.16.0)

New selfupdate package: version parsing, audit state file, updater with
Gitea registry V2 check, docker pull + compose rewrite + compose up flow.

- API: /api/selfupdate/{status,check,update} with session+bearer auth
- UI: Settings "Verzió és frissítés" card with check/install buttons + JS polling
- Scheduler: periodic check (6h default) + optional daily auto-update
- Notifications: success/failure on post-update startup verification
- Alert: info banner when update available
- docker-compose.yml: add directory bind mount for compose file access

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

controller/internal/web/handlers.go

@@ -906,6 +906,25 @@ func (s *Server) settingsData() map[string]interface{} {
 	data["MonitoringEnabled"] = s.cfg.Monitoring.Enabled
 	data["HealthchecksBase"] = s.cfg.Monitoring.HealthchecksBase
 	data["HubEnabled"] = s.cfg.Hub.Enabled
+
+	// Self-update status
+	data["SelfUpdateEnabled"] = s.cfg.SelfUpdate.Enabled
+	if s.updater != nil {
+		status := s.updater.GetStatus()
+		data["UpdateRunning"] = status.Running
+		if status.LastCheck != nil {
+			data["UpdateAvailable"] = status.LastCheck.UpdateAvailable
+			data["LatestVersion"] = status.LastCheck.LatestVersion
+			data["LastCheckTime"] = status.LastCheck.CheckedAt
+			data["LastCheckError"] = status.LastCheck.Error
+		}
+		if status.LastState != nil {
+			data["LastUpdateState"] = status.LastState
+		}
+		data["AutoUpdateEnabled"] = s.cfg.SelfUpdate.AutoUpdate
+		data["AutoUpdateTime"] = s.cfg.SelfUpdate.AutoUpdateTime
+	}
+
 	data["NotificationPrefs"] = s.settings.GetNotificationPrefs()
 
 	// Storage paths with display data