feat: add bounty page search bar

[MolhamHamwi]

Summary

• add a debounced search input to the bounties page
• filter bounties by title, description, category, org/repo, and skills
• add clear-search behavior and search-aware empty-state messaging
• add missing shared frontend utility modules required by the current app build

Closes #823

Test Plan

• npm run build

Notes

• Existing bounty-board tests reference legacy components under components/bounties/* that are absent on main; I did not change those unrelated test imports.

[Copilot]

Pull request overview

Adds a debounced search input to the /bounties page that filters loaded bounties by title, description, category, org/repo, and skills, with a clear button and search-aware empty-state messaging. Also introduces shared lib/utils.ts and lib/animations.ts modules that several existing components already import.

Changes:

• Add Search/clear UI and 250ms debounced query state to BountyGrid, with client-side filtering via a new bountyMatchesQuery helper.
• Update the empty-state copy to be search-aware while keeping existing skill/status filter behavior.
• Add frontend/src/lib/utils.ts (LANG_COLORS, formatCurrency, timeAgo, timeLeft) and frontend/src/lib/animations.ts (framer-motion variants) consumed by bounty/home/profile/leaderboard components.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
frontend/src/components/bounty/BountyGrid.tsx	Adds debounced search input, clear button, client-side filtering, and search-aware empty state.
frontend/src/lib/utils.ts	New shared utilities (LANG_COLORS, formatCurrency, timeAgo, timeLeft) referenced by existing components.
frontend/src/lib/animations.ts	New shared framer-motion Variants used across pages and components.

[MolhamHamwi]

Follow-up update: addressed the Copilot search-scope concern in 1306dfe by routing active search queries through the backend /api/bounties/search endpoint via listBounties (q, status, skill, pagination) instead of filtering only the already-loaded client pages. The grid now receives server-search paginated results, so the empty state and Load More behavior reflect the full matching result set rather than just locally loaded cards.