mara: the two cards were neither centered nor filling the space in
two-column mode. Dropped the page's own max-width entirely — Panel
already has no width opinion, and once both cards are equal-width
flex children there's no reason for an extra cap between them and
.shell-body's own 60em/centered column. Removed the now-pointless
wrapper div along with it.
Checked centered + filling behaviour at both a normal (1200px) and an
ultra-wide (1600px) viewport, and narrow-viewport stacking still
works.
1207a0e282