`MenuSubTrigger` was the only interactive menu primitive without a cursor:
`MenuItem`, `MenuCheckboxItem`, and `MenuRadioItem` all set `cursor-pointer`
plus `data-disabled:cursor-not-allowed`, so it kept the default arrow and read
as inert.

It always was clickable — clicking opens the submenu — and it is now also an
action in the add-surface menu, where the arrow cursor was actively
misleading. Fixed in the primitive rather than at that one call site, since
the gap applies to the other two submenu triggers (Diff scope, preview
Appearance) as well.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>