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-broadcast-update/responsesAreSame.d.ts

@@ -0,0 +1,14 @@
+import './_version.js';
+/**
+ * Given two `Response's`, compares several header values to see if they are
+ * the same or not.
+ *
+ * @param {Response} firstResponse
+ * @param {Response} secondResponse
+ * @param {Array<string>} headersToCheck
+ * @return {boolean}
+ *
+ * @memberof workbox-broadcast-update
+ */
+declare const responsesAreSame: (firstResponse: Response, secondResponse: Response, headersToCheck: string[]) => boolean;
+export { responsesAreSame };