Add PWA support for iOS home screen install

- Web app manifest (standalone display, NOMAD branding, icons)
- Service worker with Workbox caching (map tiles, API, uploads, CDN)
- SVG app icon + PNG generation script via sharp
- Apple meta tags (web-app-capable, black-translucent status bar)
- Dynamic theme-color for dark/light mode
- Safe area insets for notch devices

.gitignore

@@ -4,6 +4,9 @@ node_modules/
 # Build output
 client/dist/
 
+# Generated PWA icons (built from SVG via prebuild)
+client/public/icons/*.png
+
 # Database
 *.db
 *.db-shm