v2.5.3 — Admin update checker & one-click self-update

- Add version check against GitHub releases in admin dashboard
- Show amber banner when a newer version is available
- One-click update: git pull + npm install + auto-restart
- Confirmation dialog with backup recommendation and data safety info
- Dark mode support for update banner
- Fix fresh DB migration: initial schema now includes all columns
- i18n: English + German translations for all update UI

client/package.json

@@ -1,6 +1,6 @@
 {
   "name": "nomad-client",
-  "version": "2.5.2",
+  "version": "2.5.3",
   "private": true,
   "type": "module",
   "scripts": {