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/leven/index.d.ts

@@ -0,0 +1,21 @@
+declare const leven: {
+	/**
+	Measure the difference between two strings.
+
+	@example
+	```
+	import leven = require('leven');
+
+	leven('cat', 'cow');
+	//=> 2
+	```
+	*/
+	(left: string, right: string): number;
+
+	// TODO: Remove this for the next major release, refactor the whole definition to:
+	// declare function leven(left: string, right: string): number;
+	// export = leven;
+	default: typeof leven;
+};
+
+export = leven;