feat(pwa): add Progressive Web App support with iOS compatibility

- Install vite-plugin-pwa and workbox-window for PWA functionality
- Configure Vite with full PWA manifest (name, icons, theme, display)
- Add service worker caching for static assets only (no API cache)
- Create app icons (192x192, 512x512, apple-touch-icon)
- Generate iOS splash screens for multiple device sizes
- Add iOS-specific meta tags (apple-mobile-web-app-capable, etc.)
- Implement InstallPWA component with dual platform support:
  - Android/Chrome: beforeinstallprompt event with custom UI
  - iOS Safari: manual installation instructions with icons
- Add dismissal logic with 7-day localStorage persistence
- Update documentation to reflect 90% project completion

PWA implementation focuses on installability and static asset caching
while avoiding offline API cache (WebRTC requires active connection).

frontend/src/App.jsx

@@ -17,6 +17,7 @@ import HistoryPage from './pages/HistoryPage';
 import ProfilePage from './pages/ProfilePage';
 import PublicProfilePage from './pages/PublicProfilePage';
 import VerificationBanner from './components/common/VerificationBanner';
+import InstallPWA from './components/pwa/InstallPWA';
 
 // Protected Route Component with Verification Banner
 const ProtectedRoute = ({ children }) => {
@@ -65,6 +66,9 @@ function App() {
   return (
     <BrowserRouter>
       <AuthProvider>
+        {/* PWA Install Prompt */}
+        <InstallPWA />
+
         <Routes>
           {/* Public Routes */}
           <Route