fix(explore): move main-link arrow from listing card to detail-page hero
Listing card click goes back to /explore/<handle> with no arrow —
visitors land on the detail page first, where they can read the
description, see the Atmosphere services and landing page, then
choose to open the project. The diagonal-arrow button-affordance
now lives on the detail-page hero card itself: when a profile has
mainLink the whole hero becomes <a target="_blank"> and the corner
disc lights up brand-blue on hover. Records without mainLink keep
the hero as a static panel so the layout doesn't visibly downgrade.
Also: replace the homepage explore CTA copy with the shorter
"Browse apps and services in the Atmosphere." line.
Made-with: Cursor