CardHeader/CardContent/CardFooter were uniformly p-6 (24px), which on
top of the mobile shell's 16px outer padding pushed form content 40px
inward — making cards feel content-shifted on a 393px viewport. Drops
to p-4 (16px) below sm and keeps p-6 from sm+ so desktop is unchanged.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>