Add round 3 candidates challenges

[ashtonanderson]

Summary

• add three Round 3 Candidates challenges and promote them to the top of the Candidates page
• keep earlier rounds below as separate Round 2 and Round 1 sections
• tighten the current-round title block only, so Round 3 subtitles sit higher without breaking wrapped titles in older rounds

Testing

• not run (UI/data update only)

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Project	Deployment	Actions	Updated (UTC)
maia-platform-frontend	Building	Preview, Comment	Mar 31, 2026 5:47pm