bug: AgentCore tool browser lab - cell #2 error

Where: labs/module4/notebooks/5_agentcore_tool_browser.ipynb

`Error: NameError: name 'AgenticRequest' is not defined`

<img width="930" height="917" alt="Image" src="https://github.com/user-attachments/assets/fe8d6e86-8ed1-48a5-bf7e-5e09b3d4a91b" />

