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/ToBigInt64.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $BigInt = GetIntrinsic('%BigInt%', true);
+var $pow = require('math-intrinsics/pow');
+
+var ToBigInt = require('./ToBigInt');
+var BigIntRemainder = require('./BigInt/remainder');
+
+var modBigInt = require('../helpers/modBigInt');
+
+// BigInt(2**63), but node v10.4-v10.8 have a bug where you can't `BigInt(x)` anything larger than MAX_SAFE_INTEGER
+var twoSixtyThree = $BigInt && (BigInt($pow(2, 32)) * BigInt($pow(2, 31)));
+
+// BigInt(2**64), but node v10.4-v10.8 have a bug where you can't `BigInt(x)` anything larger than MAX_SAFE_INTEGER
+var twoSixtyFour = $BigInt && (BigInt($pow(2, 32)) * BigInt($pow(2, 32)));
+
+// https://262.ecma-international.org/11.0/#sec-tobigint64
+
+module.exports = function ToBigInt64(argument) {
+	var n = ToBigInt(argument);
+	var int64bit = modBigInt(BigIntRemainder, n, twoSixtyFour);
+	return int64bit >= twoSixtyThree ? int64bit - twoSixtyFour : int64bit;
+};