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/2024/AdvanceStringIndex.js

@@ -0,0 +1,30 @@
+'use strict';
+
+var CodePointAt = require('./CodePointAt');
+
+var $TypeError = require('es-errors/type');
+var isInteger = require('math-intrinsics/isInteger');
+var MAX_SAFE_INTEGER = require('math-intrinsics/constants/maxSafeInteger');
+
+// https://262.ecma-international.org/12.0/#sec-advancestringindex
+
+module.exports = function AdvanceStringIndex(S, index, unicode) {
+	if (typeof S !== 'string') {
+		throw new $TypeError('Assertion failed: `S` must be a String');
+	}
+	if (!isInteger(index) || index < 0 || index > MAX_SAFE_INTEGER) {
+		throw new $TypeError('Assertion failed: `length` must be an integer >= 0 and <= 2**53');
+	}
+	if (typeof unicode !== 'boolean') {
+		throw new $TypeError('Assertion failed: `unicode` must be a Boolean');
+	}
+	if (!unicode) {
+		return index + 1;
+	}
+	var length = S.length;
+	if ((index + 1) >= length) {
+		return index + 1;
+	}
+	var cp = CodePointAt(S, index);
+	return index + cp['[[CodeUnitCount]]'];
+};