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/es-abstract/helpers/isSamePropertyDescriptor.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var every = require('./every');
+
+module.exports = function isSamePropertyDescriptor(ES, D1, D2) {
+	var fields = [
+		'[[Configurable]]',
+		'[[Enumerable]]',
+		'[[Get]]',
+		'[[Set]]',
+		'[[Value]]',
+		'[[Writable]]'
+	];
+	return every(fields, function (field) {
+		if ((field in D1) !== (field in D2)) {
+			return false;
+		}
+		return ES.SameValue(D1[field], D2[field]);
+	});
+};