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/has-property-descriptors/index.js

@@ -0,0 +1,22 @@
+'use strict';
+
+var $defineProperty = require('es-define-property');
+
+var hasPropertyDescriptors = function hasPropertyDescriptors() {
+	return !!$defineProperty;
+};
+
+hasPropertyDescriptors.hasArrayLengthDefineBug = function hasArrayLengthDefineBug() {
+	// node v0.6 has a bug where array lengths can be Set but not Defined
+	if (!$defineProperty) {
+		return null;
+	}
+	try {
+		return $defineProperty([], 'length', { value: 1 }).length !== 1;
+	} catch (e) {
+		// In Firefox 4-22, defining length on an array throws an exception.
+		return true;
+	}
+};
+
+module.exports = hasPropertyDescriptors;