v2.5.6: Open-Meteo weather, WebSocket fixes, admin improvements

- Replace OpenWeatherMap with Open-Meteo (no API key needed)
  - 16-day forecast (up from 5 days)
  - Historical climate averages as fallback beyond 16 days
  - Auto-upgrade from climate to real forecast when available
- Fix Vacay WebSocket sync across devices (socket-ID exclusion instead of user-ID)
- Add GitHub release history tab in admin panel
- Show cluster count "1" for single map markers when zoomed out
- Add weather info panel in admin settings (replaces OpenWeatherMap key input)
- Update i18n translations (DE + EN)

server/package.json

@@ -1,6 +1,6 @@
 {
   "name": "nomad-server",
-  "version": "2.5.5",
+  "version": "2.5.6",
   "main": "src/index.js",
   "scripts": {
     "start": "node src/index.js",