Opening a row's details inside a tool group left an unpainted band the
size of the growth: the group's MaskedView hosts the list inside a
SwiftUI mask whose native bounds kept the old height, so everything
past it was clipped even though layout and accessibility frames were
right. Draw the scroll-edge fades as screen-colored gradients over a
plain clipped view instead, and read the group's content size from
LegendList's layout so the outer row resizes in the same commit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>