Add progressive web app companion for cross-platform access

Vite + TypeScript PWA that mirrors the Android app's core features:
- Pre-processed shelter data (build-time UTM33N→WGS84 conversion)
- Leaflet map with shelter markers, user location, and offline tiles
- Canvas compass arrow (ported from DirectionArrowView.kt)
- IndexedDB shelter cache with 7-day staleness check
- Service worker with CacheFirst tiles and precached app shell
- i18n for en, nb, nn (ported from Android strings.xml)
- iOS/Android compass handling with low-pass filter
- Respects user map interaction (no auto-snap on pan/zoom)
- Build revision cache-breaker for reliable SW updates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pwa/node_modules/workbox-recipes/offlineFallback.d.ts

@@ -0,0 +1,18 @@
+import './_version.js';
+export interface OfflineFallbackOptions {
+    pageFallback?: string;
+    imageFallback?: string;
+    fontFallback?: string;
+}
+/**
+ * An implementation of the [comprehensive fallbacks recipe]{@link https://developers.google.com/web/tools/workbox/guides/advanced-recipes#comprehensive_fallbacks}. Be sure to include the fallbacks in your precache injection
+ *
+ * @memberof workbox-recipes
+ *
+ * @param {Object} [options]
+ * @param {string} [options.pageFallback] Precache name to match for pag fallbacks. Defaults to offline.html
+ * @param {string} [options.imageFallback] Precache name to match for image fallbacks.
+ * @param {string} [options.fontFallback] Precache name to match for font fallbacks.
+ */
+declare function offlineFallback(options?: OfflineFallbackOptions): void;
+export { offlineFallback };