feat(events,session): add React-friendly subscribe APIs and snapshot getters

Adds backwards-compatible primitives needed to consume the renderer from
React 19 hooks (useSyncExternalStore, use(), TanStack Query) without
re-architecting the event bus.

- EventDispatcher.subscribe(type, cb): () => void — unsubscriber-returning
  wrapper matching the useSyncExternalStore subscribe signature.
- CommunicationManager.subscribeMessage(eventCtor, handler): () => void —
  packet-stream equivalent.
- SessionDataManager.getUserDataSnapshot() and
  RoomSessionManager.getActiveRoomSessionSnapshot() — referentially-stable
  read-only views invalidated through new SESSION_DATA_UPDATED and
  ROOM_SESSION_UPDATED events.

All additive; existing addEventListener/removeEventListener / IRoomSession
APIs are unchanged. Bumps renderer to 2.1.0.

packages/communication/src/CommunicationManager.ts

@@ -203,6 +203,17 @@ export class CommunicationManager implements ICommunicationManager
         this._connection.removeMessageEvent(event);
     }
 
+    public subscribeMessage<T extends IMessageEvent>(eventCtor: new (callback: (event: T) => void) => T, handler: (event: T) => void): () => void
+    {
+        if(!eventCtor || !handler) return () => {};
+
+        const event = new eventCtor(handler);
+
+        this.registerMessageEvent(event);
+
+        return () => this.removeMessageEvent(event);
+    }
+
     public get connection(): IConnection
     {
         return this._connection;