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-strategies/index.d.ts

@@ -0,0 +1,20 @@
+import { CacheFirst } from './CacheFirst.js';
+import { CacheOnly } from './CacheOnly.js';
+import { NetworkFirst, NetworkFirstOptions } from './NetworkFirst.js';
+import { NetworkOnly, NetworkOnlyOptions } from './NetworkOnly.js';
+import { StaleWhileRevalidate } from './StaleWhileRevalidate.js';
+import { Strategy, StrategyOptions } from './Strategy.js';
+import { StrategyHandler } from './StrategyHandler.js';
+import './_version.js';
+declare global {
+    interface FetchEvent {
+        readonly preloadResponse: Promise<any>;
+    }
+}
+/**
+ * There are common caching strategies that most service workers will need
+ * and use. This module provides simple implementations of these strategies.
+ *
+ * @module workbox-strategies
+ */
+export { CacheFirst, CacheOnly, NetworkFirst, NetworkFirstOptions, NetworkOnly, NetworkOnlyOptions, StaleWhileRevalidate, Strategy, StrategyHandler, StrategyOptions, };