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-navigation-preload/index.d.ts

@@ -0,0 +1,23 @@
+import { disable } from './disable.js';
+import { enable } from './enable.js';
+import { isSupported } from './isSupported.js';
+import './_version.js';
+interface NavigationPreloadState {
+    enabled?: boolean;
+    headerValue?: string;
+}
+interface NavigationPreloadManager {
+    disable(): Promise<void>;
+    enable(): Promise<void>;
+    getState(): Promise<NavigationPreloadState>;
+    setHeaderValue(value: string): Promise<void>;
+}
+declare global {
+    interface ServiceWorkerRegistration {
+        readonly navigationPreload: NavigationPreloadManager;
+    }
+}
+/**
+ * @module workbox-navigation-preload
+ */
+export { disable, enable, isSupported };