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-window/utils/WorkboxEventTarget.d.ts

@@ -0,0 +1,37 @@
+import { WorkboxEvent, WorkboxEventMap } from './WorkboxEvent.js';
+export type ListenerCallback = (event: WorkboxEvent<any>) => any;
+/**
+ * A minimal `EventTarget` shim.
+ * This is necessary because not all browsers support constructable
+ * `EventTarget`, so using a real `EventTarget` will error.
+ * @private
+ */
+export declare class WorkboxEventTarget {
+    private readonly _eventListenerRegistry;
+    /**
+     * @param {string} type
+     * @param {Function} listener
+     * @private
+     */
+    addEventListener<K extends keyof WorkboxEventMap>(type: K, listener: (event: WorkboxEventMap[K]) => any): void;
+    /**
+     * @param {string} type
+     * @param {Function} listener
+     * @private
+     */
+    removeEventListener<K extends keyof WorkboxEventMap>(type: K, listener: (event: WorkboxEventMap[K]) => any): void;
+    /**
+     * @param {Object} event
+     * @private
+     */
+    dispatchEvent(event: WorkboxEvent<any>): void;
+    /**
+     * Returns a Set of listeners associated with the passed event type.
+     * If no handlers have been registered, an empty Set is returned.
+     *
+     * @param {string} type The event type.
+     * @return {Set<ListenerCallback>} An array of handler functions.
+     * @private
+     */
+    private _getEventListenersByType;
+}