fix: store executor and monitor tasks to prevent garbage collection

dashboard/backend/main.py

@@ -39,20 +39,24 @@ async def lifespan(app: FastAPI):
 
     # Start agent executor service
     from services import agent_executor
+    executor_task = None
     try:
-        asyncio.create_task(agent_executor.start_executor())
+        executor_task = asyncio.create_task(agent_executor.start_executor())
         print("Agent executor service started")
     except Exception as e:
         print(f"Failed to start agent executor: {e}")
         import traceback
         traceback.print_exc()
 
-    asyncio.create_task(monitor_containers())
+    monitor_task = asyncio.create_task(monitor_containers())
 
     yield
 
     # Shutdown
     print("=== Application Shutdown ===")
+    if executor_task:
+        executor_task.cancel()
+    monitor_task.cancel()
 
 limiter = Limiter(key_func=get_remote_address)
 app = FastAPI(title="NAS Dashboard", lifespan=lifespan)