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/IsStringPrefix.js

@@ -0,0 +1,43 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var isPrefixOf = require('../helpers/isPrefixOf');
+
+// var callBound = require('call-bound');
+
+// var $charAt = callBound('String.prototype.charAt');
+
+// https://262.ecma-international.org/9.0/#sec-isstringprefix
+
+module.exports = function IsStringPrefix(p, q) {
+	if (typeof p !== 'string') {
+		throw new $TypeError('Assertion failed: "p" must be a String');
+	}
+
+	if (typeof q !== 'string') {
+		throw new $TypeError('Assertion failed: "q" must be a String');
+	}
+
+	return isPrefixOf(p, q);
+	/*
+	if (p === q || p === '') {
+		return true;
+	}
+
+	var pLength = p.length;
+	var qLength = q.length;
+	if (pLength >= qLength) {
+		return false;
+	}
+
+	// assert: pLength < qLength
+
+	for (var i = 0; i < pLength; i += 1) {
+		if ($charAt(p, i) !== $charAt(q, i)) {
+			return false;
+		}
+	}
+	return true;
+	*/
+};