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/2023/StringIndexOf.js

@@ -0,0 +1,36 @@
+'use strict';
+
+var callBound = require('call-bound');
+
+var $TypeError = require('es-errors/type');
+var isInteger = require('math-intrinsics/isInteger');
+
+var $slice = callBound('String.prototype.slice');
+
+// https://262.ecma-international.org/12.0/#sec-stringindexof
+
+module.exports = function StringIndexOf(string, searchValue, fromIndex) {
+	if (typeof string !== 'string') {
+		throw new $TypeError('Assertion failed: `string` must be a String');
+	}
+	if (typeof searchValue !== 'string') {
+		throw new $TypeError('Assertion failed: `searchValue` must be a String');
+	}
+	if (!isInteger(fromIndex) || fromIndex < 0) {
+		throw new $TypeError('Assertion failed: `fromIndex` must be a non-negative integer');
+	}
+
+	var len = string.length;
+	if (searchValue === '' && fromIndex <= len) {
+		return fromIndex;
+	}
+
+	var searchLen = searchValue.length;
+	for (var i = fromIndex; i <= (len - searchLen); i += 1) {
+		var candidate = $slice(string, i, i + searchLen);
+		if (candidate === searchValue) {
+			return i;
+		}
+	}
+	return -1;
+};