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-precaching/getCacheKeyForURL.d.ts

@@ -0,0 +1,22 @@
+import './_version.js';
+/**
+ * Takes in a URL, and returns the corresponding URL that could be used to
+ * lookup the entry in the precache.
+ *
+ * If a relative URL is provided, the location of the service worker file will
+ * be used as the base.
+ *
+ * For precached entries without revision information, the cache key will be the
+ * same as the original URL.
+ *
+ * For precached entries with revision information, the cache key will be the
+ * original URL with the addition of a query parameter used for keeping track of
+ * the revision info.
+ *
+ * @param {string} url The URL whose cache key to look up.
+ * @return {string} The cache key that corresponds to that URL.
+ *
+ * @memberof workbox-precaching
+ */
+declare function getCacheKeyForURL(url: string): string | undefined;
+export { getCacheKeyForURL };