rethink the right-side units list/cost display
It has numerous issues:
- it's hidden by default on medium/small screens, or mobile. Our first tester couldn't see it when splitscreening at work, and work is an important use case.
- our first tester couldn't figure out how to show it while it's hidden. There's a button, but I guess it's not obvious.
- cost display doesn't make sense at first.
- I'm not sure how well related-units will scale, especially if something costs many different currencies.