feat: mobile responsive polish for bounty cards, nav, and hero (Closes #833)

[orgy272]

Summary

Mobile responsive polish for bounty cards, navbar mobile behavior, and hero readability at 375px and 768px breakpoints.

What changed

• frontend/src/components/bounty/BountyCard.tsx
  • Reduced mobile padding
  • Changed reward/meta row to stack on small screens
  • Allowed metadata chips to wrap on narrow widths
  • Moved status badge to flow layout on mobile and absolute only on sm+
• frontend/src/components/bounty/BountyGrid.tsx
  • Made header controls wrap cleanly on mobile
  • Constrained status filter width on small screens
• frontend/src/components/home/HeroSection.tsx
  • Improved terminal readability on small screens (text-xs, tighter command string)
  • Made live stats strip wrap with responsive spacing to prevent overflow at 375px
• frontend/src/components/layout/Navbar.tsx
  • Auto-close hamburger and profile dropdown on route change for consistent mobile navigation behavior

Acceptance fit

• Bounty cards now stack and wrap cleanly on mobile
• Hamburger state behaves correctly through navigation
• Hero terminal + stats are readable at small widths
• Horizontal overflow sources addressed in component layout

Closes #833

Wallet: 61FYMEPXMe73ypR53wMAR7PYAWHhZWKFJMNKnG9NwoW

[orgy272]

Pushed follow-up CI-unblock fixes on this branch as well:

• restored frontend/src/lib/animations.ts and frontend/src/lib/utils.ts
• fixed .gitignore from lib/ to /lib/ so frontend/src/lib stays tracked

This targets the frontend TypeScript/Build module-not-found failures seen in the previous run.

[orgy272]

CI is green for project checks after latest fixes; remaining red is AI Code Review / trigger-review failing with GitHub API 403 rate-limit inside repository automation (API rate limit exceeded for user ID ...).

This failure is external to PR code changes and requires rate-limit reset or maintainer/admin rerun rights.