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/2015/ToDateString.js

@@ -0,0 +1,21 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $TypeError = require('es-errors/type');
+var $Date = GetIntrinsic('%Date%');
+var $String = GetIntrinsic('%String%');
+
+var $isNaN = require('math-intrinsics/isNaN');
+
+// https://262.ecma-international.org/6.0/#sec-todatestring
+
+module.exports = function ToDateString(tv) {
+	if (typeof tv !== 'number') {
+		throw new $TypeError('Assertion failed: `tv` must be a Number');
+	}
+	if ($isNaN(tv)) {
+		return 'Invalid Date';
+	}
+	return $String(new $Date(tv));
+};