Handle the layout properly

[matt-dray]

What's the correct mixture of bslib::layout_columns() and bslib::layout_colum_wrap() to achieve this in the main area of the app (to mimic inputs at first)? Maintain flexibility becuase we may add to or amend the layout later.

[matt-dray]

I'm seeing this kind of gap appear sometimes, though perhaps that's just in the Positron viewer (this example went away when I opened in browser). No, I've seen it in the browser too.