feat: implement polished reusable Bounty Card component

[automaton365-sys]

Implemented the Bounty Card component requirements from issue #1 with reusable props and responsive Tailwind UI.

What I changed

• Kept component props reusable (, , , , )
• Added improved responsive layout and hover effects
• Styled difficulty badge for all levels with light/dark support
• Added clearer reward hierarchy label
• Added progress clamping () to avoid invalid bar widths
• Added subtle progress bar animation and dark mode track color

Validation

mergefund-hackathon-kit@0.1.0 lint
next lint

./src/components/leaderboard.tsx
46:13 Warning: Using <img> could result in slower LCP and higher bandwidth. Consider using <Image /> from next/image or a custom image loader to automatically optimize images. This may incur additional usage or cost from your provider. See: https://nextjs.org/docs/messages/no-img-element @next/next/no-img-element

info - Need to disable some ESLint rules? Learn more here: https://nextjs.org/docs/app/api-reference/config/eslint#disabling-rules passes (existing unrelated warning in only)

Fixes #1
/claim #1