This PR adds a link indicator to the `Current Plan: ...` entry in the
user menu

<img width="232" alt="link_indicator"
src="https://github.com/user-attachments/assets/89c6247c-08cb-4cac-b136-5c5b71f1a975"
/>

to indicate this opens an external link and not something within Zed.

Release Notes:

- N/A