Add search bar to bounties page

[nguyenquockhang1610]

Closes #823

Summary

• Add a debounced search input to the bounties grid
• Filter loaded bounties by title, description, category, repo metadata, URLs, and skill tags
• Add a clear search button and search-aware empty state messaging
• Restore missing frontend lib helpers used by the current app so the frontend build passes

Test

• npm run build

Wallet: 7P1RPGmct2eWAVnqmgQDXofuKThYJQVNhRatRbZ7nzjn