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/docker-compose.yml

@@ -14,9 +14,11 @@ services:
     volumes:
       # Docker socket — required for compose operations + DB dumps (docker exec)
       - /var/run/docker.sock:/var/run/docker.sock
-      # Controller config
+      # Controller directory (compose file access for self-update)
+      - /opt/docker/felhom-controller:/opt/docker/felhom-controller
+      # Controller config (read-only override on top of directory mount)
       - /opt/docker/felhom-controller/controller.yaml:/opt/docker/felhom-controller/controller.yaml:ro
-      # Controller persistent data (sessions, restic cache, restic password)
+      # Controller persistent data (named volume override on top of directory mount)
       - controller-data:/opt/docker/felhom-controller/data
       # Stack compose files (read + write for git sync)
       - /opt/docker/stacks:/opt/docker/stacks