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-core/copyResponse.d.ts

@@ -0,0 +1,22 @@
+import './_version.js';
+/**
+ * Allows developers to copy a response and modify its `headers`, `status`,
+ * or `statusText` values (the values settable via a
+ * [`ResponseInit`]{@link https://developer.mozilla.org/en-US/docs/Web/API/Response/Response#Syntax}
+ * object in the constructor).
+ * To modify these values, pass a function as the second argument. That
+ * function will be invoked with a single object with the response properties
+ * `{headers, status, statusText}`. The return value of this function will
+ * be used as the `ResponseInit` for the new `Response`. To change the values
+ * either modify the passed parameter(s) and return it, or return a totally
+ * new object.
+ *
+ * This method is intentionally limited to same-origin responses, regardless of
+ * whether CORS was used or not.
+ *
+ * @param {Response} response
+ * @param {Function} modifier
+ * @memberof workbox-core
+ */
+declare function copyResponse(response: Response, modifier?: (responseInit: ResponseInit) => ResponseInit): Promise<Response>;
+export { copyResponse };