fix(durable-demo): remove task_id from POST response (internal detail)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: RaviPidaparthi

sdk/agentserver/azure-ai-agentserver-invocations/samples/durable-agent-demo/README.md

@@ -123,7 +123,7 @@ curl -s -X POST "${ENDPOINT}/invocations?api-version=2025-11-15-preview&agent_se
 
 Response (202):
 ```json
-{"status": "started", "invocation_id": "inv_abc123...", "session_id": "demo-...", "task_id": "research-demo-..."}
+{"status": "started", "invocation_id": "inv_abc123...", "session_id": "demo-..."}
 ```
 
 Save the invocation ID:

sdk/agentserver/azure-ai-agentserver-invocations/samples/durable-agent-demo/src/durable-research-agent/app.py

@@ -91,7 +91,6 @@ async def _crash():
             "status": status,
             "invocation_id": invocation_id,
             "session_id": session_id,
-            "task_id": task_id,
         },
         status_code=202,
     )