test: add unit tests for accessibility, search UI, and utility functi…

[PeterOche]

Description

This PR resolves several open issues addressing search UI empty states, utility unit test coverage, and hook debounce reuse:

• Search Empty State (Show an empty-state on the search page when there are no results #1295):

  • Rendered an accessible empty-state message and actionable filter/query suggestions in SearchResultsVisualizer when search returns 0 matches.
  • Added accessibility attributes (role="status", aria-live="polite", data-testid="search-empty-state", aria-hidden="true" on the icon).
  • Wrapped AdvancedSearchInterface in a Next.js Suspense boundary in src/app/search/page.tsx.
  • Added unit test suite in SearchResultsVisualizer.test.tsx.

• Accessibility Utilities Unit Tests (Add unit tests for the accessibility utilities #1296):

  • Added unit test suite in src/utils/tests/accessibilityUtils.test.ts covering contrast calculations, focusability, roving focus candidates, focus trapping, accessible names, screen reader announcements, and WCAG audit checks.
  • Added 3-digit shorthand hex code support in hexToRgb.

• Notification Utilities Unit Tests (Add unit tests for the notification utilities #1297):

  • Added comprehensive unit test suite in src/utils/tests/notificationUtils.test.ts covering timestamp formatting, quiet hours calculations, delivery decisions, analytics aggregation, sorting, filtering, date grouping, preference validation, and default preference generation.
  • Added defensive guards against invalid timestamp formats and malformed preferences.

• Shared Debounce in Search Filters Hook (Reuse the shared debounce utility in the search-filters hook #1293):

  • Added cancellation support (.cancel()) to debounce in src/utils/formUtils.ts.
  • Refactored useSearchFilters.tsx to replace inline setTimeout/clearTimeout timers with the shared debounce utility.
  • Added unit tests for debounce and throttle in src/utils/tests/formUtils.test.ts.

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Related Issues

• Closes Reuse the shared debounce utility in the search-filters hook #1293
• Closes Show an empty-state on the search page when there are no results #1295
• Closes Add unit tests for the accessibility utilities #1296
• Closes Add unit tests for the notification utilities #1297

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Files Changed

• src/app/search/page.tsx
• src/components/search/SearchResultsVisualizer.tsx
• src/components/search/__tests__/SearchResultsVisualizer.test.tsx
• src/utils/accessibilityUtils.ts
• src/utils/tests/accessibilityUtils.test.ts
• src/utils/notificationUtils.ts
• src/utils/tests/notificationUtils.test.ts
• src/utils/formUtils.ts
• src/hooks/useSearchFilters.tsx
• src/utils/tests/formUtils.test.ts

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Checklist

• Implemented across all target files
• Unit/integration tests added and covering happy paths and edge cases
• No regressions; follows project coding conventions

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