Implement reusable bounty card component

[youfuwang888-tech]

Pull Request Draft

Summary

Implements a reusable responsive BountyCard component for the Bounty Card Component bounty.

Changes

• Adds a typed BountyCardProps interface.
• Displays title, reward, tags, difficulty, and progress.
• Adds optional description and due-date style label for richer card content.
• Formats rewards as USD currency.
• Clamps progress values to the valid 0-100 range.
• Adds accessible progress bar attributes.
• Improves mobile and desktop card layout.
• Adds hover styling with Tailwind transitions.

Verification

To verify locally:

npm install
npm run lint
npm run dev

Open:

http://localhost:3000/bounty-card

Check desktop and mobile layouts, hover state, progress bars, and browser console.

Notes

This PR focuses only on the bounty card component and demo page. It does not introduce external services, wallet logic, authentication, or payment flows.