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/2021/ToIndex.js

@@ -0,0 +1,24 @@
+'use strict';
+
+var $RangeError = require('es-errors/range');
+
+var ToIntegerOrInfinity = require('./ToIntegerOrInfinity');
+var ToLength = require('./ToLength');
+var SameValue = require('./SameValue');
+
+// https://262.ecma-international.org/8.0/#sec-toindex
+
+module.exports = function ToIndex(value) {
+	if (typeof value === 'undefined') {
+		return 0;
+	}
+	var integerIndex = ToIntegerOrInfinity(value);
+	if (integerIndex < 0) {
+		throw new $RangeError('index must be >= 0');
+	}
+	var index = ToLength(integerIndex);
+	if (!SameValue(integerIndex, index)) {
+		throw new $RangeError('index must be >= 0 and < 2 ** 53 - 1');
+	}
+	return index;
+};