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/notify/notifier.go

@@ -242,6 +242,18 @@ func (n *Notifier) NotifyIntegrityFailed(message, details string) {
 	n.Notify("integrity_failed", "warning", message, details)
 }
 
+// NotifyUpdateSuccess sends a notification about a successful controller update.
+func (n *Notifier) NotifyUpdateSuccess(fromVer, toVer string) {
+	n.Notify("update_success", "info",
+		fmt.Sprintf("Controller frissítve: %s → %s", fromVer, toVer), "")
+}
+
+// NotifyUpdateFailed sends a notification about a failed controller update.
+func (n *Notifier) NotifyUpdateFailed(targetVer, errMsg string) {
+	n.Notify("update_failed", "warning",
+		fmt.Sprintf("Controller frissítés sikertelen: %s — %s", targetVer, errMsg), "")
+}
+
 // SendTest sends a test notification for verifying the notification flow.
 func (n *Notifier) SendTest() error {
 	if !n.enabled {