fix(site): large left-aligned feature icons to match the mockup (#379)

Lay out each landing feature as icon | divider | text — a 64px icon on the
left, a full-height vertical rule, then heading + description — instead of a
small icon stacked on top. Pure CSS grid (divider via ::before), with
smaller icon/gaps on mobile so the text stays readable.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>