Replace `min-vh-100` with `dvh` to better support mobile

[brian-smith-tcril]

frontend-base/shell/DefaultLayout.tsx

Line 6 in 8a42bd5

<div className="d-flex flex-column min-vh-100">

uses 100vh (via min-vh-100). vh doesn't account for mobile UI elements.

I made a Paragon issue for adding min-dvh-* utility classes

• Add min-dvh-* utility class paragon#3985

Once that's discussed/lands then updating this to use the new dvh class would be awesome.