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/SetIntegrityLevel.js

@@ -0,0 +1,57 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $SyntaxError = require('es-errors/syntax');
+var $TypeError = require('es-errors/type');
+var isObject = require('es-object-atoms/isObject');
+var $gOPD = require('gopd');
+var $preventExtensions = GetIntrinsic('%Object.preventExtensions%', true);
+var $gOPN = GetIntrinsic('%Object.getOwnPropertyNames%', true);
+
+var forEach = require('../helpers/forEach');
+
+var DefinePropertyOrThrow = require('./DefinePropertyOrThrow');
+var IsAccessorDescriptor = require('./IsAccessorDescriptor');
+var ToPropertyDescriptor = require('./ToPropertyDescriptor');
+
+// https://262.ecma-international.org/6.0/#sec-setintegritylevel
+
+module.exports = function SetIntegrityLevel(O, level) {
+	if (!isObject(O)) {
+		throw new $TypeError('Assertion failed: Type(O) is not Object');
+	}
+	if (level !== 'sealed' && level !== 'frozen') {
+		throw new $TypeError('Assertion failed: `level` must be `"sealed"` or `"frozen"`');
+	}
+	if (!$preventExtensions) {
+		throw new $SyntaxError('SetIntegrityLevel requires native `Object.preventExtensions` support');
+	}
+	var status = $preventExtensions(O);
+	if (!status) {
+		return false;
+	}
+	if (!$gOPN) {
+		throw new $SyntaxError('SetIntegrityLevel requires native `Object.getOwnPropertyNames` support');
+	}
+	var theKeys = $gOPN(O);
+	if (level === 'sealed') {
+		forEach(theKeys, function (k) {
+			DefinePropertyOrThrow(O, k, { configurable: false });
+		});
+	} else if (level === 'frozen') {
+		forEach(theKeys, function (k) {
+			var currentDesc = $gOPD(O, k);
+			if (typeof currentDesc !== 'undefined') {
+				var desc;
+				if (IsAccessorDescriptor(ToPropertyDescriptor(currentDesc))) {
+					desc = { configurable: false };
+				} else {
+					desc = { configurable: false, writable: false };
+				}
+				DefinePropertyOrThrow(O, k, desc);
+			}
+		});
+	}
+	return true;
+};