feat: Complete PWA implementation with offline support and install prompts

PWA Features Implemented:
✅ Offline Fallback Page (/offline)
  - User-friendly offline page with connection status
  - Auto-redirect when back online
  - Lists available offline features
  - Retry and home navigation buttons

✅ Install Prompt UI (InstallPrompt component)
  - beforeinstallprompt event handler for Android/Desktop
  - iOS-specific install instructions with Share icon
  - Smart dismissal with 7-day cooldown
  - Already-installed detection

✅ Background Sync for Pending Actions
  - useBackgroundSync hook with multiple sync triggers
  - Periodic sync every 5 minutes when online
  - Sync on tab visibility change
  - Service Worker sync registration
  - BackgroundSyncProvider integration

✅ next-pwa Configuration Updates
  - Offline fallback to /offline page
  - Network timeout (10s) for better offline detection
  - skipWaiting and clientsClaim enabled
  - Runtime caching with NetworkFirst strategy

Files Created:
- app/offline/page.tsx (131 lines)
- components/pwa/InstallPrompt.tsx (164 lines)
- hooks/useBackgroundSync.ts (71 lines)
- components/providers/BackgroundSyncProvider.tsx (10 lines)

Files Modified:
- app/layout.tsx (added InstallPrompt and BackgroundSyncProvider)
- next.config.mjs (offline fallback + workbox options)

Total: 376 new lines across 4 new files + 2 modified files

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

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

maternal-web/next.config.mjs

@@ -13,6 +13,9 @@ const pwaConfig = withPWA({
   register: true,
   skipWaiting: true,
   disable: process.env.NODE_ENV === 'development',
+  fallbacks: {
+    document: '/offline',
+  },
   runtimeCaching: [
     {
       urlPattern: /^https?.*/,
@@ -22,9 +25,14 @@ const pwaConfig = withPWA({
         expiration: {
           maxEntries: 200,
         },
+        networkTimeoutSeconds: 10,
       },
     },
   ],
+  workboxOptions: {
+    skipWaiting: true,
+    clientsClaim: true,
+  },
 });
 
 export default pwaConfig(nextConfig);