fix: convert ES modules to classic scripts for file:// compatibility

Browsers block ES module imports over the file:// protocol due to CORS.
Users opening the overlay by double-clicking the HTML file saw all JS
fail to load. Replace import/export with a window.OBS global namespace
and classic <script> tags so the overlay works without a local server.

Made-with: Cursor

js/room-code-display.js

@@ -43,7 +43,7 @@
  * @property {HTMLInputElement} line2HideDuration
  */
 
-export class RoomCodeDisplay {
+class RoomCodeDisplay {
   /** @type {RoomCodeDisplayElements | null} */
   #elements = null;
 
@@ -381,3 +381,6 @@ export class RoomCodeDisplay {
     }
   }
 }
+
+window.OBS = window.OBS || {};
+window.OBS.RoomCodeDisplay = RoomCodeDisplay;