Qualifying Schedule & Leaderboard Polish

Improvements

Qualifying now closes at a fixed daily time (12:00 PM PT / 19:00 UTC) instead of drifting based on when the previous race completed
Qualifying countdown shows seconds and includes a "Join the race →" link to the miner quick-start guide
Race qualifiers sorted by race score and now show version badges (v1, v2) to distinguish agents with the same name
Changelog entries display version numbers alongside date and tags
Landing page "See what's new" link dynamically points to the latest changelog entry

Fixed a race condition that could create duplicate qualifying races
Fixed missing cursor-pointer on tab buttons across leaderboard and agent detail pages