feat(agent-office): notification broadcast + telegram tracking + activity feed API

- Add WebSocket notification messages for task_assigned/task_completed
- Structure telegram send_message return value with ok/message_id
- Track telegram delivery status in task result_data
- Add test_telegram command to stock agent
- Add GET /api/agent-office/activity unified feed endpoint

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

agent-office/app/websocket_manager.py

@@ -43,4 +43,13 @@ class WebSocketManager:
     async def send_agent_move(self, agent_id: str, target: str) -> None:
         await self.broadcast({"type": "agent_move", "agent": agent_id, "target": target})
 
+    async def send_notification(self, agent_id: str, event: str, task_id: str = None, message: str = "") -> None:
+        await self.broadcast({
+            "type": "notification",
+            "agent": agent_id,
+            "event": event,
+            "task_id": task_id,
+            "message": message,
+        })
+
 ws_manager = WebSocketManager()