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/websocket-client.js

@@ -10,7 +10,7 @@ const INITIAL_RECONNECT_DELAY_MS = 1_000;
  * @typedef {'connecting'|'connected'|'disconnected'|'error'} WsConnectionState
  */
 
-export class WebSocketClient {
+class WebSocketClient {
   constructor(options = {}) {
     const {
       onStatusChange = () => {},
@@ -466,3 +466,6 @@ export class WebSocketClient {
     }, delay);
   }
 }
+
+window.OBS = window.OBS || {};
+window.OBS.WebSocketClient = WebSocketClient;