When min-brightness is set, a scroll step that would cross it was not
clamped — only scrolling while already at or below min was blocked.
With scroll-step: 5 and min-brightness: 1, scrolling from 5% would
pass the guard (5 > 1) and set brightness to 0%.
Fix by computing the post-step value before applying it: if it would
fall below min-brightness, set exactly to min-brightness instead.
