Add search filtering to bounties page

[yjr24300180030]

Summary

• add a debounced search input to the bounties grid
• filter loaded bounties by title, description, category, tier, status, repo/org, and skills
• add missing frontend shared lib modules so the page and build resolve existing imports
• add a regression test for search filtering and clearing

Verification

• npm test -- bounty-grid-search.test.tsx
• npm run build

Wallet

Solana: 93xYERDhNDTdWRNUBXromRpxKPKeT93uV89iijEFGy4r

Closes #823