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/async-function/legacy.js

@@ -0,0 +1,18 @@
+'use strict';
+
+/** @type {import('.').AsyncFunctionConstructor | false} */
+var cached;
+
+/** @type {import('.')} */
+module.exports = function getAsyncFunction() {
+	if (typeof cached === 'undefined') {
+		try {
+			// eslint-disable-next-line no-new-func
+			cached = Function('return async function () {}')().constructor;
+		} catch (e) {
+			cached = false;
+		}
+	}
+	return cached;
+};
+