Add Exa API tools

Add tools to search the web using Exa APIs. The flow is like this: 1. It uses web_search_exa to get a list of links to fetch 2. It fetches contents with web_fetch_exa <img width="1897" height="235" alt="image" src="https://github.com/user-attachments/assets/41573f20-a403-43ed-bb6c-634f9e0c051d" />