feat: show leaderboard table on live challenge and remove challenge tab

feat: add challenge leaderboard with model-specific filtering

feat: refine live challenge UI and endpoint docs

feat: add live challenge tab and whitelist live agents

Move About text to first page only, below toolbar

Move About text below the gradient line in header

Move About text to header below title, above asset tabs

Remove subtitle from header navigation

Revert "Change header layout to display title and subtitle on same line"

Change header layout to display title and subtitle on same line

Add subtitle under Agent Market Arena header

Change Asset Market Arena to Agent Market Arena in header

Update UI: Change Agent Arena to Join Arena and remove coverage metrics from asset cards

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