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/2019/CanonicalNumericIndexString.js

@@ -0,0 +1,19 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var SameValue = require('./SameValue');
+var ToNumber = require('./ToNumber');
+var ToString = require('./ToString');
+
+// https://262.ecma-international.org/6.0/#sec-canonicalnumericindexstring
+
+module.exports = function CanonicalNumericIndexString(argument) {
+	if (typeof argument !== 'string') {
+		throw new $TypeError('Assertion failed: `argument` must be a String');
+	}
+	if (argument === '-0') { return -0; }
+	var n = ToNumber(argument);
+	if (SameValue(ToString(n), argument)) { return n; }
+	return void 0;
+};