UX has changed as their is no longer a  "+Add Signals Button"

Path: /weave/guides/evaluation/monitors

Need to update documentation to not reference "+Add Signals" as the UI has changed.

<img width="1676" height="913" alt="Image" src="https://github.com/user-attachments/assets/5e381295-3dce-41a1-880c-b4f50e2cd194" />