fix(websocket): remove export{} from sharedworker entry point, rename worker

- Remove `export {}` which caused webpack to tree-shake the entire
  SharedWorker bundle, resulting in an empty JS file with no connect
  handler — root cause of WebSocket never opening
- Rename SharedWorker instance from 'notification-worker' to
  'notification-worker-ws' to force browser to create a fresh worker
  instance instead of reusing a cached empty one

web_src/js/features/websocket.sharedworker.ts

@@ -1,7 +1,5 @@
 // One WebSocket connection per URL, shared across all tabs via SharedWorker.
 // Messages from the server are JSON objects broadcast to all connected ports.
-export {}; // make this a module to avoid global scope conflicts with other sharedworker files
-
 const RECONNECT_DELAY_INITIAL = 50;
 const RECONNECT_DELAY_MAX = 10000;