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-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "nomad-client",
-  "version": "2.5.1",
+  "version": "2.5.2",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "nomad-client",
-      "version": "2.5.1",
+      "version": "2.5.2",
       "dependencies": {
         "@react-pdf/renderer": "^4.3.2",
         "axios": "^1.6.7",