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/nitro/session/ISessionDataManager.ts

@@ -3,6 +3,7 @@ import { IFurnitureData } from './IFurnitureData';
 import { IGroupInformationManager } from './IGroupInformationManager';
 import { IIgnoredUsersManager } from './IIgnoredUsersManager';
 import { IProductData } from './IProductData';
+import { IUserDataSnapshot } from './IUserDataSnapshot';
 
 export interface ISessionDataManager
 {
@@ -53,4 +54,5 @@ export interface ISessionDataManager
     isCameraFollowDisabled: boolean;
     uiFlags: number;
     tags: string[];
+    getUserDataSnapshot(): Readonly<IUserDataSnapshot>;
 }