R1:c019f76283ce

Make profile menu full-height

Summary:
Ref T10054. This makes the profile menu full-height. It uses two pieces of dark magic:

- `calc()`, which allows you to do math in CSS.
- The `vh` unit, which is CSS for "viewport height".

Apparently this kind of stuff just works now? CSS got good at some point?

Test Plan:
- Page looks correct in Safari, Chrome, Firefox.
- Checked `caniuse.com` for `vh` and `calc()`, saw they're supported?

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10054…