Get Live Scoreboard

Return the cached global ranking, recomputing on a cache miss.

When the realtime subsystem is disabled there is no cache to read and no worker keeping it warm, but the ranking is still a plain DB computation — serve it directly from Postgres instead of failing the public view.

show_live_leaderboard gates it: the switch used to hide the scoreboard in the SPA while this endpoint served the standings to anyone who asked.