Show more actualités in the homepage "À la une" section

Bumped from 5 to 12 posts (2-column card grid instead of a single
stacked list) now that there are 41 real actualités to draw from,
plus a "Voir toutes les actualités" link at the end of the section.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
