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-expiration/models/CacheTimestampsModel.d.ts

@@ -0,0 +1,77 @@
+import '../_version.js';
+/**
+ * Returns the timestamp model.
+ *
+ * @private
+ */
+declare class CacheTimestampsModel {
+    private readonly _cacheName;
+    private _db;
+    /**
+     *
+     * @param {string} cacheName
+     *
+     * @private
+     */
+    constructor(cacheName: string);
+    /**
+     * Performs an upgrade of indexedDB.
+     *
+     * @param {IDBPDatabase<CacheDbSchema>} db
+     *
+     * @private
+     */
+    private _upgradeDb;
+    /**
+     * Performs an upgrade of indexedDB and deletes deprecated DBs.
+     *
+     * @param {IDBPDatabase<CacheDbSchema>} db
+     *
+     * @private
+     */
+    private _upgradeDbAndDeleteOldDbs;
+    /**
+     * @param {string} url
+     * @param {number} timestamp
+     *
+     * @private
+     */
+    setTimestamp(url: string, timestamp: number): Promise<void>;
+    /**
+     * Returns the timestamp stored for a given URL.
+     *
+     * @param {string} url
+     * @return {number | undefined}
+     *
+     * @private
+     */
+    getTimestamp(url: string): Promise<number | undefined>;
+    /**
+     * Iterates through all the entries in the object store (from newest to
+     * oldest) and removes entries once either `maxCount` is reached or the
+     * entry's timestamp is less than `minTimestamp`.
+     *
+     * @param {number} minTimestamp
+     * @param {number} maxCount
+     * @return {Array<string>}
+     *
+     * @private
+     */
+    expireEntries(minTimestamp: number, maxCount?: number): Promise<string[]>;
+    /**
+     * Takes a URL and returns an ID that will be unique in the object store.
+     *
+     * @param {string} url
+     * @return {string}
+     *
+     * @private
+     */
+    private _getId;
+    /**
+     * Returns an open connection to the database.
+     *
+     * @private
+     */
+    private getDb;
+}
+export { CacheTimestampsModel };