leaderboard: lock GT row + header in a capped gallery scroll box

leaderboard: fixed 4-sample gallery, auto-size iframe, center modal

leaderboard: rename tabs, relabel fixtures as samples, inline gallery row stats

leaderboard: show edit-diff turntable in gallery grid for editing fixtures

Serve rotating WebP turntables + GT generator

gallery: searchable fixture picker, URL-persisted picks, cached render proxies

add visual Gallery tab (top-10 verified, sticky GT, fixture picker)