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/2025/CodePointAt.js

@@ -0,0 +1,55 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+var callBound = require('call-bound');
+var isLeadingSurrogate = require('../helpers/isLeadingSurrogate');
+var isTrailingSurrogate = require('../helpers/isTrailingSurrogate');
+
+var UTF16SurrogatePairToCodePoint = require('./UTF16SurrogatePairToCodePoint');
+
+var $charAt = callBound('String.prototype.charAt');
+var $charCodeAt = callBound('String.prototype.charCodeAt');
+
+// https://262.ecma-international.org/12.0/#sec-codepointat
+
+module.exports = function CodePointAt(string, position) {
+	if (typeof string !== 'string') {
+		throw new $TypeError('Assertion failed: `string` must be a String');
+	}
+	var size = string.length;
+	if (position < 0 || position >= size) {
+		throw new $TypeError('Assertion failed: `position` must be >= 0, and < the length of `string`');
+	}
+	var first = $charCodeAt(string, position);
+	var cp = $charAt(string, position);
+	var firstIsLeading = isLeadingSurrogate(first);
+	var firstIsTrailing = isTrailingSurrogate(first);
+	if (!firstIsLeading && !firstIsTrailing) {
+		return {
+			'[[CodePoint]]': cp,
+			'[[CodeUnitCount]]': 1,
+			'[[IsUnpairedSurrogate]]': false
+		};
+	}
+	if (firstIsTrailing || (position + 1 === size)) {
+		return {
+			'[[CodePoint]]': cp,
+			'[[CodeUnitCount]]': 1,
+			'[[IsUnpairedSurrogate]]': true
+		};
+	}
+	var second = $charCodeAt(string, position + 1);
+	if (!isTrailingSurrogate(second)) {
+		return {
+			'[[CodePoint]]': cp,
+			'[[CodeUnitCount]]': 1,
+			'[[IsUnpairedSurrogate]]': true
+		};
+	}
+
+	return {
+		'[[CodePoint]]': UTF16SurrogatePairToCodePoint(first, second),
+		'[[CodeUnitCount]]': 2,
+		'[[IsUnpairedSurrogate]]': false
+	};
+};