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-broadcast-update/BroadcastUpdatePlugin.js

@@ -0,0 +1,51 @@
+/*
+  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 { dontWaitFor } from 'workbox-core/_private/dontWaitFor.js';
+import { BroadcastCacheUpdate, } from './BroadcastCacheUpdate.js';
+import './_version.js';
+/**
+ * This plugin will automatically broadcast a message whenever a cached response
+ * is updated.
+ *
+ * @memberof workbox-broadcast-update
+ */
+class BroadcastUpdatePlugin {
+    /**
+     * Construct a {@link workbox-broadcast-update.BroadcastUpdate} instance with
+     * the passed options and calls its `notifyIfUpdated` method whenever the
+     * plugin's `cacheDidUpdate` callback is invoked.
+     *
+     * @param {Object} [options]
+     * @param {Array<string>} [options.headersToCheck=['content-length', 'etag', 'last-modified']]
+     *     A list of headers that will be used to determine whether the responses
+     *     differ.
+     * @param {string} [options.generatePayload] A function whose return value
+     *     will be used as the `payload` field in any cache update messages sent
+     *     to the window clients.
+     */
+    constructor(options) {
+        /**
+         * A "lifecycle" callback that will be triggered automatically by the
+         * `workbox-sw` and `workbox-runtime-caching` handlers when an entry is
+         * added to a cache.
+         *
+         * @private
+         * @param {Object} options The input object to this function.
+         * @param {string} options.cacheName Name of the cache being updated.
+         * @param {Response} [options.oldResponse] The previous cached value, if any.
+         * @param {Response} options.newResponse The new value in the cache.
+         * @param {Request} options.request The request that triggered the update.
+         * @param {Request} options.event The event that triggered the update.
+         */
+        this.cacheDidUpdate = async (options) => {
+            dontWaitFor(this._broadcastUpdate.notifyIfUpdated(options));
+        };
+        this._broadcastUpdate = new BroadcastCacheUpdate(options);
+    }
+}
+export { BroadcastUpdatePlugin };