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/NumberToBigInt.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $BigInt = GetIntrinsic('%BigInt%', true);
+var $RangeError = require('es-errors/range');
+var $SyntaxError = require('es-errors/syntax');
+var $TypeError = require('es-errors/type');
+
+var isInteger = require('math-intrinsics/isInteger');
+
+// https://262.ecma-international.org/12.0/#sec-numbertobigint
+
+module.exports = function NumberToBigInt(number) {
+	if (typeof number !== 'number') {
+		throw new $TypeError('Assertion failed: `number` must be a String');
+	}
+	if (!isInteger(number)) {
+		throw new $RangeError('The number ' + number + ' cannot be converted to a BigInt because it is not an integer');
+	}
+	if (!$BigInt) {
+		throw new $SyntaxError('BigInts are not supported in this environment');
+	}
+	return $BigInt(number);
+};