PHUIBoxView: Consistently set CSS border-radius to 3px
Summary:
Don't set `border-radius: 5px` for the `WHITE_CONFIG` variant but `border-radius: 3px` for any other variant as there are no obvious reasons.
This mitigates (but does not fix) a small UI issue in the box bottom corners looking unclosed.
Closes T16204
Test Plan: Go to a page rendering a PHUIBoxView like http://phorge.localhost/settings/panel/apitokens/, preferably after setting Dark Mode in the user's Display Preferences to have more contrast, and look at the previously unclosed rounded corners at the bottom of the box.
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T16204
Differential Revision: https://we.phorge.it/D26231