docs: Add note about using batch_get for reliability

The search endpoint has a known issue (OpenHands/OpenHands#13121).
Recommend using batch_get by ID when the conversation ID is known.

Co-authored-by: openhands <openhands@all-hands.dev>

Author: openhands-agent

openhands/usage/cloud/cloud-api.mdx

@@ -171,6 +171,11 @@ Each update is streamed as it occurs, allowing you to provide real-time feedback
 
 After starting a conversation, you can check its status to monitor whether the agent has completed its task.
 
+<Note>
+  If you know the conversation ID, use the batch get endpoint (`GET /api/v1/app-conversations?ids=...`) 
+  to retrieve status directly. This is the most reliable method.
+</Note>
+
 #### Step 1: Check Start Task Status
 
 When you start a conversation, you receive a start task ID. Poll this endpoint until `status` becomes `READY` and `app_conversation_id` is available: