test(pwa): add comprehensive PWA and Vitest test suite
- Install Vitest and React Testing Library for frontend tests
- Configure Vitest with jsdom environment and coverage
- Add test setup file with global mocks (matchMedia, IntersectionObserver)
- Write InstallPWA component tests (14 tests):
- iOS detection and manual installation instructions
- Android/Chrome beforeinstallprompt event handling
- Install and dismiss functionality
- 7-day dismissal persistence (localStorage)
- Installed state detection (standalone mode)
- Write PWA configuration tests (28 tests):
- App icons existence (PNG and SVG)
- iOS splash screens for multiple devices
- Vite PWA plugin configuration
- index.html meta tags (iOS PWA support)
- Manifest schema validation
- Service worker configuration (Workbox)
- Write service worker tests (24 tests):
- Service worker registration and lifecycle
- Workbox integration
- Cache Storage API operations
- Migrate existing WebRTC tests from Jest to Vitest (25 tests):
- Update imports to use Vitest (vi.fn, describe, it, expect)
- Fix WebRTCWarning and webrtcDetection test expectations
- Add test scripts to package.json (test, test:watch, test:ui, test:coverage)
All 91 tests passing (InstallPWA: 14, PWA config: 28, Service Worker: 24,
WebRTC: 25 total across 2 files)
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