feat(build): bundle frontend with vite and matrix-js-sdk, fix HOST in server.js

public/app.js

@@ -1,6 +1,4 @@
-/* gibbz voice POC — WebRTC mesh voice + screen share + spatial audio.
-   POC shortcuts: no auth (voice), no E2E crypto (matrix text), single audio context. */
-import * as matrixcs from 'https://cdn.jsdelivr.net/npm/matrix-js-sdk@42.4.0/lib/browser-index.min.js';
+import * as matrixcs from 'matrix-js-sdk';
 
 // ---------------------------------------------------------------------------
 // state