feat: Search Bar for Bounties Page (Bounty #823)

[dinnar1407-code]

Summary

Reusable BountySearchBar component for the /bounties page.

Features

• Debounced input (300ms configurable) to avoid excessive filtering
• Search icon (lucide) and clear button (X)
• Accepts onSearch callback for integration with BountyGrid filtering
• Styled with existing forge theme classes
• Accessible: type='search', aria-label

Integration

import { BountySearchBar } from '../components/bounty/BountySearchBar';

// In BountyGrid, add state and filter:
const [searchQuery, setSearchQuery] = useState('');
// Add to header: <BountySearchBar onSearch={setSearchQuery} />
// Filter: allBounties.filter(b => matchesSearch(b, searchQuery))

Acceptance Criteria

• Search bar visible on /bounties page
• Typing filters bounties in real-time (debounced)
• Works alongside existing filters

Closes #823