fix hiding of horizontal line in start page

[efferre79]

No description provided.

[chennes]

The reason for putting the element in the layout below was so that it was wider than the First Start box (I was trying to give a clearer visual separator between that region and the "Don't show again" checkbox). I'm not convinced that even in its current incarnation it's serving that purposed, and in the proposed location it's probably entirely superfluous. @FreeCAD/design-working-group do you have any ideas for how to handle the problem of ensuring the checkbox clearly applies to the whole Start screen, and not just the First Start box?

[obelisk79]

I would probably hold off on this. I'm working through a few other things, but I believe the whole page needs quite a few adjustments before 1.0 goes out the door. I would suggest a tabbed layout for separating the settings bit and the regular start parts. I can mock up a layout, but it will probably be a week before I manage to do so.

[maxwxyz]

@efferre79 I guess the proposal needs some more discussion but just a heads up for the upcoming feature freeze:
If you want this draft PR to be considered for a version 1.0 release, it should be marked ready for review by Monday, 2024-06-03 at the latest. (further details in the 1.0 feature freeze forum announcement).