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)

frontend/vite.config.js

@@ -1,6 +1,7 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 import { VitePWA } from 'vite-plugin-pwa'
+import path from 'path'
 
 // Parse allowed hosts from environment variable
 const getAllowedHosts = () => {
@@ -95,4 +96,20 @@ export default defineConfig({
       clientPort: 8080,
     },
   },
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    setupFiles: './src/test/setup.js',
+    css: true,
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'json', 'html'],
+      exclude: [
+        'node_modules/',
+        'src/test/',
+        '**/*.config.js',
+        '**/*.config.ts',
+      ],
+    },
+  },
 })