Add round 4 candidates challenges

[ashtonanderson]

Summary

• add three Round 4 Candidates challenges and promote them to the top of the Candidates page
• keep earlier rounds below as separate Round 3, Round 2, and Round 1 sections
• remove the compact title treatment from the current round so longer Round 4 titles wrap cleanly

Testing

• not run (UI/data update only)

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Project	Deployment	Actions	Updated (UTC)
maia-platform-frontend	Building	Preview, Comment	Apr 1, 2026 5:42pm