Add search bar to bounties page

[lxidzc]

Closes #823

Summary

• Add a debounced search input to the bounties page.
• Filter loaded bounties by title, description, and skills/tags.
• Add a clear button for resetting the search query.
• Preserve existing status and language filters.

Tests

• npm test -- BountyGrid.test.tsx
• npm run build

[lxidzc]

Solana wallet for bounty payout: 8nEwim8LjDSU2v2PSUMzJxQ4ms3WwKCCfT1z5ysz55j8