Apply global visual polish across the web client: corner-shape:
superellipse(1.5) with corner-shape: round pairing for full circles,
elevation tokens that draw 0.5px stroke outlines inside box-shadow for
floating surfaces, 0.5px hairline borders and divider lines for
neutral-token strokes, and tuned stroke contrast plus larger radii for
menus, settings panels, and cards. Stylesheet-scan specs in ui-theme
reject unpaired circles, border+shadow mixes, and 1px neutral hairlines
repo-wide.
Closes#3287
imccyu