fix(workshop): expose Polymarket on the hub

[maruthiprithivi]

Summary

• show AI SRE and Polymarket as separate cards on the workshop domain root
• link each card directly to its dedicated track landing
• retain the existing Real-Time Market Analytics workshop card
• use a responsive three/two/one-column card grid

Verification

• TypeScript check passed
• production build passed
• desktop and mobile browser QA passed
• all three card labels and hrefs verified; no console errors

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