Follow up to https://github.com/zed-industries/zed/pull/45440 adding an
item for "Open Thread as Markdown" and another for scroll to top and
scroll to bottom.

<img width="500" height="646" alt="Screenshot 2025-12-23 at 1  12@2x"
src="https://github.com/user-attachments/assets/c82e26bb-c255-4d73-b733-ef6ea269fabe"
/>

Release Notes:

- N/A