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/api/src/communication/ICommunicationManager.ts

@@ -6,5 +6,6 @@ export interface ICommunicationManager
     init(): Promise<void>;
     registerMessageEvent(event: IMessageEvent): IMessageEvent;
     removeMessageEvent(event: IMessageEvent): void;
+    subscribeMessage<T extends IMessageEvent>(eventCtor: new (callback: (event: T) => void) => T, handler: (event: T) => void): () => void;
     connection: IConnection;
 }