fix: resolve mobile viewport overflow on article pages

fix: resolve mobile viewport overflow on article pages

Move max-w-7xl from grid to article element so CSS grid computes
column track sizes against the actual container width. Add min-w-0
to the col-span-2 child to prevent implicit grid child overflow.
Simplify .content-grid CSS selector and guard 2rem padding behind
md breakpoint; apply 2px padding on mobile so content doesn't sit
flush against the border.

Co-Authored-By: Claude Haiku 4.5 <redacted>