feat(FN-4177): add heartbeat messaging support for chat rooms

The merge delivers room heartbeat messaging for agents, allowing heartbeat-triggered agents to send messages into chat rooms and subscribe to room activity. Core changes include new chat-store room APIs, engine heartbeat room message tools, and corresponding tests, with a small dashboard ChatView up

Fusion-Task-Id: FN-4177

packages/engine/src/runtimes/__tests__/in-process-runtime.test.ts

@@ -542,6 +542,7 @@ describe("InProcessRuntime", () => {
       await runtime.start();
       const monitor = runtime.getHeartbeatMonitor();
       expect(monitor).toBeDefined();
+      expect(monitor?.getChatStore()).toBeDefined();
     }, 30000);
 
     // Regression: heartbeat auto-claim path was warning