pet.trezy.setPreferences

Save a text style, either for the whole account or for one device. ⚠ `scope` IS REQUIRED AND HAS NO DEFAULT. Guessing it is the one mistake that cannot be undone by guessing again: silently defaulting to `account` changes the typeface on every device somebody owns when they meant to change one, and silently defaulting to `device` leaves them wondering why their laptop never followed. The client always knows which the player asked for, because the player was asked.