Fix: Watch Together Raum-Erstellung + Download-Button

- Server/Frontend Protokoll-Mismatch behoben (create_room, join_room, room_created, room_joined, playback_state)
- togglePlay sendet jetzt korrekt pause/resume statt toggle_play
- Download-Button: SPA-Fallback fuer /downloads/ verhindert, 404 statt Reload
- download-Attribut am Link hinzugefuegt

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/App.tsx

@@ -134,6 +134,7 @@ export default function App() {
             <a
               className="hub-download-btn"
               href="/downloads/GamingHub-Setup.exe"
+              download
               title="Desktop App herunterladen"
             >
               {'\u2B07\uFE0F'}