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/2022/IsConstructor.js

@@ -0,0 +1,40 @@
+'use strict';
+
+var GetIntrinsic = require('../GetIntrinsic.js');
+
+var $construct = GetIntrinsic('%Reflect.construct%', true);
+
+var DefinePropertyOrThrow = require('./DefinePropertyOrThrow');
+try {
+	DefinePropertyOrThrow({}, '', { '[[Get]]': function () {} });
+} catch (e) {
+	// Accessor properties aren't supported
+	DefinePropertyOrThrow = null;
+}
+
+// https://262.ecma-international.org/6.0/#sec-isconstructor
+
+if (DefinePropertyOrThrow && $construct) {
+	var isConstructorMarker = {};
+	var badArrayLike = {};
+	DefinePropertyOrThrow(badArrayLike, 'length', {
+		'[[Get]]': function () {
+			throw isConstructorMarker;
+		},
+		'[[Enumerable]]': true
+	});
+
+	module.exports = function IsConstructor(argument) {
+		try {
+			// `Reflect.construct` invokes `IsConstructor(target)` before `Get(args, 'length')`:
+			$construct(argument, badArrayLike);
+		} catch (err) {
+			return err === isConstructorMarker;
+		}
+	};
+} else {
+	module.exports = function IsConstructor(argument) {
+		// unfortunately there's no way to truly check this without try/catch `new argument` in old environments
+		return typeof argument === 'function' && !!argument.prototype;
+	};
+}