UX: Allow First Aid (or hotkeyed skills) to be 'a'pplied but have nothing happen if not usable
New 'a'pply skills UI only allows ability to choose usable skills, but you can't tell if you can use First Aid unless you open the UI
As a habitual First Aid apply-er, I always map First Aid to '0' and hit a0 after every fight. In the latest version, if you haven't been injured you can't use the skill, so hitting a0 will bring up the skills window, but do nothing - I then have to hit escape to exit out of it. Since there's no way to tell if First Aid is usable without opening the skills window, it's becoming a bit tedious (a second or two wasted every time it happens, but several times per floor). The main issue isn't whether or not the skill is used, but that the skills window stays open.
It would be nice if First Aid could be used any time, but it would give you a "You have no wounds that can be healed right now" message. Alternatively, any skills assigned to hotkeys (0-9) should always be used, but say "You cannot use that skill right now" if it's not usable. I have no strong opinions on whether or not this should waste a turn. Or even if the skills window just closed if you hit a number from 0-9 with no message.