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/ToBigInt.js

@@ -0,0 +1,51 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $BigInt = GetIntrinsic('%BigInt%', true);
+var $Number = GetIntrinsic('%Number%');
+var $TypeError = require('es-errors/type');
+var $SyntaxError = require('es-errors/syntax');
+
+var StringToBigInt = require('./StringToBigInt');
+var ToPrimitive = require('./ToPrimitive');
+
+// https://262.ecma-international.org/13.0/#sec-tobigint
+
+module.exports = function ToBigInt(argument) {
+	if (!$BigInt) {
+		throw new $SyntaxError('BigInts are not supported in this environment');
+	}
+
+	var prim = ToPrimitive(argument, $Number);
+
+	if (prim == null) {
+		throw new $TypeError('Cannot convert null or undefined to a BigInt');
+	}
+
+	if (typeof prim === 'boolean') {
+		return prim ? $BigInt(1) : $BigInt(0);
+	}
+
+	if (typeof prim === 'number') {
+		throw new $TypeError('Cannot convert a Number value to a BigInt');
+	}
+
+	if (typeof prim === 'string') {
+		var n = StringToBigInt(prim);
+		if (typeof n === 'undefined') {
+			throw new $TypeError('Failed to parse String to BigInt');
+		}
+		return n;
+	}
+
+	if (typeof prim === 'symbol') {
+		throw new $TypeError('Cannot convert a Symbol value to a BigInt');
+	}
+
+	if (typeof prim !== 'bigint') {
+		throw new $SyntaxError('Assertion failed: unknown primitive type');
+	}
+
+	return prim;
+};