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-background-sync/BackgroundSyncPlugin.js

@@ -0,0 +1,36 @@
+/*
+  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 { Queue } from './Queue.js';
+import './_version.js';
+/**
+ * A class implementing the `fetchDidFail` lifecycle callback. This makes it
+ * easier to add failed requests to a background sync Queue.
+ *
+ * @memberof workbox-background-sync
+ */
+class BackgroundSyncPlugin {
+    /**
+     * @param {string} name See the {@link workbox-background-sync.Queue}
+     *     documentation for parameter details.
+     * @param {Object} [options] See the
+     *     {@link workbox-background-sync.Queue} documentation for
+     *     parameter details.
+     */
+    constructor(name, options) {
+        /**
+         * @param {Object} options
+         * @param {Request} options.request
+         * @private
+         */
+        this.fetchDidFail = async ({ request }) => {
+            await this._queue.pushRequest({ request });
+        };
+        this._queue = new Queue(name, options);
+    }
+}
+export { BackgroundSyncPlugin };