The welcome card switched layout on the screen's width, so a small card on
a wide screen squeezed the greeting and four shortcuts side by side. It now
lays itself out by its own width (a container query): shortcuts in two
columns under the greeting when small, four in a row when there's room,
and beside the greeting when it's wide. In aurora.css, so the themes need
no rebuild.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>