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/2020/IsDataDescriptor.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var hasOwn = require('hasown');
+
+var isPropertyDescriptor = require('../helpers/records/property-descriptor');
+
+// https://262.ecma-international.org/5.1/#sec-8.10.2
+
+module.exports = function IsDataDescriptor(Desc) {
+	if (typeof Desc === 'undefined') {
+		return false;
+	}
+
+	if (!isPropertyDescriptor(Desc)) {
+		throw new $TypeError('Assertion failed: `Desc` must be a Property Descriptor');
+	}
+
+	if (!hasOwn(Desc, '[[Value]]') && !hasOwn(Desc, '[[Writable]]')) {
+		return false;
+	}
+
+	return true;
+};