Allow renaming chat sessions

Testing #258320

If chat sessions are going to longer lived and we want the user to be managing multiple at the same time, we should support renaming them. You should be able to use F2 (or enter) on mac to rename in place like the explorer, and right click to rename:

<img width="507" height="189" alt="Image" src="https://github.com/user-attachments/assets/2ffc53d7-c8f3-4507-a326-7b6bbbf11846" />