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/index.d.ts

@@ -0,0 +1,25 @@
+import { BackgroundSyncPlugin } from './BackgroundSyncPlugin.js';
+import { Queue, QueueOptions } from './Queue.js';
+import { QueueStore } from './QueueStore.js';
+import { StorableRequest } from './StorableRequest.js';
+import './_version.js';
+interface SyncManager {
+    getTags(): Promise<string[]>;
+    register(tag: string): Promise<void>;
+}
+declare global {
+    interface ServiceWorkerRegistration {
+        readonly sync: SyncManager;
+    }
+    interface SyncEvent extends ExtendableEvent {
+        readonly lastChance: boolean;
+        readonly tag: string;
+    }
+    interface ServiceWorkerGlobalScopeEventMap {
+        sync: SyncEvent;
+    }
+}
+/**
+ * @module workbox-background-sync
+ */
+export { BackgroundSyncPlugin, Queue, QueueOptions, QueueStore, StorableRequest };