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/utils/deleteOutdatedCaches.js

@@ -0,0 +1,38 @@
+/*
+  Copyright 2018 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+import '../_version.js';
+const SUBSTRING_TO_FIND = '-precache-';
+/**
+ * Cleans up incompatible precaches that were created by older versions of
+ * Workbox, by a service worker registered under the current scope.
+ *
+ * This is meant to be called as part of the `activate` event.
+ *
+ * This should be safe to use as long as you don't include `substringToFind`
+ * (defaulting to `-precache-`) in your non-precache cache names.
+ *
+ * @param {string} currentPrecacheName The cache name currently in use for
+ * precaching. This cache won't be deleted.
+ * @param {string} [substringToFind='-precache-'] Cache names which include this
+ * substring will be deleted (excluding `currentPrecacheName`).
+ * @return {Array<string>} A list of all the cache names that were deleted.
+ *
+ * @private
+ * @memberof workbox-precaching
+ */
+const deleteOutdatedCaches = async (currentPrecacheName, substringToFind = SUBSTRING_TO_FIND) => {
+    const cacheNames = await self.caches.keys();
+    const cacheNamesToDelete = cacheNames.filter((cacheName) => {
+        return (cacheName.includes(substringToFind) &&
+            cacheName.includes(self.registration.scope) &&
+            cacheName !== currentPrecacheName);
+    });
+    await Promise.all(cacheNamesToDelete.map((cacheName) => self.caches.delete(cacheName)));
+    return cacheNamesToDelete;
+};
+export { deleteOutdatedCaches };