Refresh landing page product flow

[maxw06]

Closes #140.

Summary

• Reposition the landing hero around on-chain work and instant payout messaging.
• Add a mobile app section with iOS and Android store links.
• Reframe the task cards around open-source bounties, tasks/gigs, and services.
• Add escrow and on-chain settlement copy to make the Solana value prop concrete.
• Fix mobile layout handling for partner logos and testimonial cards.

Verification

• npm run build
• Desktop browser check at 1280px:
  • no document-level horizontal overflow
  • mobile app section present
  • App Store and Google Play links present
  • escrow/on-chain settlement copy present
• Mobile browser check at 390px:
  • no document-level horizontal overflow
  • mobile app section present
  • Download the app CTA present
  • App Store and Google Play links present

Screenshots

• Desktop 1280px
• Mobile 390px

Notes

The store links used in the implementation:

• iOS: https://apps.apple.com/us/app/gibwork/id6757281508
• Android: https://play.google.com/store/apps/details?id=com.gibwork.app

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