Add Progressive Web App functionality

- Add web app manifest for home screen installation
- Implement service worker with offline caching strategy
- Create offline fallback page with auto-reconnect
- Generate PWA icons in multiple sizes (72px-512px)
- Add PWA meta tags and Apple Touch icons to all pages
- Register service worker with graceful degradation
- Update documentation with PWA installation instructions
- Add browserconfig.xml for Windows tile support

Features:
- Installable on mobile and desktop
- Offline functionality with cached resources
- App-like experience in standalone mode
- Automatic updates when online
- Works seamlessly with existing progressive enhancement

🤖 Generated with [Claude Code](https://claude.ai/code)

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

README.md

@@ -6,6 +6,7 @@ A community-driven web application for tracking winter road conditions and icy h
 
 - 🗺️ **Interactive Map** - Real-time location tracking centered on Grand Rapids
 - ⚡ **Fast Geocoding** - Lightning-fast address lookup with Mapbox API
+- 📱 **Progressive Web App** - Install on mobile home screen, works offline
 - 🚫 **JavaScript-Free Mode** - Complete functionality without JavaScript via server-side rendering
 - 🖼️ **Static Maps** - Auto-generated Mapbox static images for non-JS users
 - 🔄 **Auto-Expiration** - Reports automatically removed after 48 hours
@@ -172,10 +173,31 @@ See `docs/deployment.md` for detailed manual deployment instructions.
 ### API Documentation
 Interactive API documentation available at `/api-docs` when running the server.
 
+## PWA Installation
+
+### Mobile Devices
+1. Open the app in your mobile browser
+2. Look for the "Add to Home Screen" prompt
+3. Tap "Add" to install the app on your home screen
+4. The app will work offline and behave like a native app
+
+### Desktop Browsers
+1. Visit the app in Chrome, Edge, or Safari
+2. Look for the install icon in the address bar
+3. Click "Install" to add the app to your desktop
+4. Launch from your applications folder or start menu
+
+### PWA Features
+- **Offline Access:** View cached reports when disconnected
+- **App-like Experience:** Standalone window, no browser UI
+- **Home Screen Icon:** Quick access like native apps
+- **Automatic Updates:** Always stay current when online
+
 ## Technology Stack
 
 - **Backend:** Node.js, Express.js, SQLite, TypeScript
-- **Frontend:** Progressive Enhancement (Vanilla JavaScript + Server-side rendering)
+- **Frontend:** Progressive Web App with Progressive Enhancement
+  - **PWA:** Installable, offline-capable, service worker caching
   - **Enhanced:** Leaflet.js interactive maps with real-time updates
   - **Fallback:** Server-side HTML tables with static Mapbox images
 - **Geocoding:** Mapbox API (with Nominatim fallback)