fix(websocket): declare sharedworker as ES module and fix port cleanup

- Add export{} to declare websocket.sharedworker.ts as an ES module,
  preventing TypeScript TS2451 redeclaration errors caused by global
  scope conflicts with eventsource.sharedworker.ts
- Always delete port from sourcesByPort on close regardless of remaining
  subscriber count, preventing MessagePort keys from leaking in the Map

web_src/js/features/websocket.sharedworker.ts

@@ -1,5 +1,7 @@
 // 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;
 
@@ -116,10 +118,10 @@ const sourcesByPort = new Map<MessagePort, WsSource>();
         const source = sourcesByPort.get(port);
         if (!source) return;
         const count = source.deregister(port);
+        sourcesByPort.delete(port);
         if (count === 0) {
           source.close();
           sourcesByUrl.delete(source.url);
-          sourcesByPort.delete(port);
         }
       } else if (event.data.type === 'status') {
         const source = sourcesByPort.get(port);