fix: restore bold text in leaderboard intro

DOI -> concept DOI (always-latest, resolves to v0.3)

v0.3: strict task-completion grader; refresh leaderboard + headline

Correct leaderboard: separate populations, exclude provider errors, fix ceiling claim

Leaderboard: force dark text in shaded family cells (readable in dark mode)

Convert Space to static leaderboard (zero CPU quota)

signalbench interactive leaderboard (static)

initial commit