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/side-channel-list/index.d.ts

@@ -0,0 +1,13 @@
+declare namespace getSideChannelList {
+	type Channel<K, V> = {
+		assert: (key: K) => void;
+		has: (key: K) => boolean;
+		get: (key: K) => V | undefined;
+		set: (key: K, value: V) => void;
+		delete: (key: K) => boolean;
+	};
+}
+
+declare function getSideChannelList<V, K>(): getSideChannelList.Channel<K, V>;
+
+export = getSideChannelList;