Adds basic table layout for the global change requests page and makes
the page accessible at `/change-requests`.
The table is based on the project-based change request table, but with a
slightly different set of columns.
Uses mock data for now.
There's still some styling to be done for the column widths and handling
narrower screens.
<img width="1386" height="671" alt="image"
src="https://github.com/user-attachments/assets/b24ed625-d3f6-4281-ba44-30744d5063f3"
/>
If the flag is disabled, we render nothing useful.
<img width="1429" height="287" alt="image"
src="https://github.com/user-attachments/assets/289b5707-4389-4c08-bf68-55d63e186ba5"
/>
closes 1-4076
