Items in asset list are not fully accessible due to missing scrollbar

1. Create a Unity project
2. Click the "AI" button
3. Click "Agree and install Unity AI"
4. Wait until the installation is complete
5. Go to the "Project" window
6. Create many different assets
7. Select them all
8. Right-click and select "Add to Assistant"
9. In the Assistant view, expand the "Attached items" list
10. Observe the view

Actual results: The asset list in the panel displays more items than can fit within the visible area, but no vertical scrollbar is shown. As a result, the bottom items are partially hidden or completely inaccessible to the user.

Expected results: When the number of items exceeds the visible panel height, a vertical scrollbar should appear, allowing the user to scroll through the list and access all items.

Reproducible with versions: 2.0.0-pre.1(6000.4.0b11, 6000.5.0a8)

Tested on (OS): macOS - Tahoe 26.3.1