feat(#67): implement search UI with filters and shortcuts

Implements comprehensive search interface for knowledge base:

Components:
- SearchInput: Debounced search with Cmd+K (Ctrl+K) shortcut
- SearchResults: Main results view with highlighted snippets
- SearchFilters: Sidebar for filtering by status and tags
- Search page: Full search experience at /knowledge/search

Features:
- Search-as-you-type with 300ms debounce
- HTML snippet highlighting (using <mark> from API)
- Tag and status filters with PDA-friendly language
- Keyboard shortcuts (Cmd+K/Ctrl+K to open, Escape to clear)
- No results state with helpful suggestions
- Loading states
- Visual status indicators (🟢 Active, 🔵 Scheduled, etc.)

Navigation:
- Added search button to header with keyboard hint
- Global Cmd+K shortcut redirects to search page
- Added "Knowledge" link to main navigation

Infrastructure:
- Updated Input component to support forwardRef for proper ref handling
- Comprehensive test coverage (100% on main components)
- All tests passing (339 passed)
- TypeScript strict mode compliant
- ESLint compliant

Fixes #67

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/scratchpads/67-search-ui.md

@@ -0,0 +1,75 @@
+# Issue #67: [KNOW-015] Search UI
+
+## Objective
+
+Build a comprehensive search interface in the Next.js web UI with search-as-you-type, filters, keyboard shortcuts, and highlighted snippets.
+
+## Approach
+
+1. Review existing web UI structure and components
+2. Design component architecture for search functionality
+3. Implement TDD workflow (RED-GREEN-REFACTOR):
+   - Write tests for search input component
+   - Implement search input with Cmd+K shortcut
+   - Write tests for search results page
+   - Implement search results with highlighting
+   - Write tests for filter sidebar
+   - Implement filter functionality
+   - Add no results state
+4. Ensure all tests pass and coverage meets 85% minimum
+5. Run quality gates and code review
+6. Commit and close issue
+
+## Component Architecture
+
+- `SearchInput` - Header search component with Cmd+K shortcut
+- `SearchResults` - Main results page/component
+- `SearchResultItem` - Individual result with highlighted snippets
+- `SearchFilters` - Sidebar for tag and status filtering
+- `NoResults` - Empty state component
+
+## Progress
+
+- [x] Create scratchpad
+- [x] Review existing web UI structure
+- [x] Write tests for SearchInput component
+- [x] Implement SearchInput with keyboard shortcut
+- [x] Write tests for SearchResults page
+- [x] Implement SearchResults page
+- [x] Write tests for SearchResultItem with highlighting
+- [x] Implement result item with snippet highlighting
+- [x] Write tests for SearchFilters
+- [x] Implement filter sidebar
+- [x] Write tests for NoResults state
+- [x] Implement no results state
+- [x] Add debounced search-as-you-type
+- [x] Create search page at /knowledge/search
+- [x] Add search button to Navigation header
+- [x] Fix Input component to support forwardRef
+- [x] All tests passing (100% coverage)
+- [x] Typecheck passing
+- [x] Lint passing
+- [ ] Run code review
+- [ ] Run QA checks
+- [ ] Commit changes
+- [ ] Close issue #67
+
+## Testing Strategy
+
+- Unit tests for all components
+- Test keyboard shortcuts (Cmd+K, Escape)
+- Test debouncing behavior
+- Test filter interactions
+- Test safe HTML rendering for highlights
+- Test no results state
+- Aim for 85%+ coverage
+
+## Notes
+
+- Use Shadcn/ui components (Input, Card, Badge, etc.)
+- Follow PDA-friendly language (no "URGENT", "MUST", etc.)
+- Use visual indicators: 🟢 Active, 🔵 Scheduled, ⏸️ Paused, 💤 Dormant, ⚪ Not started
+- Safely render HTML snippets from API (use dangerouslySetInnerHTML with sanitization or a library)
+- Debounce search input to avoid excessive API calls
+- Cmd+K should open search modal/focus search input
+- Escape should close search modal if open