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-range-requests/utils/parseRangeHeader.d.ts

@@ -0,0 +1,14 @@
+import '../_version.js';
+/**
+ * @param {string} rangeHeader A Range: header value.
+ * @return {Object} An object with `start` and `end` properties, reflecting
+ * the parsed value of the Range: header. If either the `start` or `end` are
+ * omitted, then `null` will be returned.
+ *
+ * @private
+ */
+declare function parseRangeHeader(rangeHeader: string): {
+    start?: number;
+    end?: number;
+};
+export { parseRangeHeader };