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/is-bigint/index.js

@@ -0,0 +1,41 @@
+'use strict';
+
+var hasBigInts = require('has-bigints')();
+
+if (hasBigInts) {
+	var bigIntValueOf = BigInt.prototype.valueOf;
+	/** @type {(value: object) => value is BigInt} */
+	var tryBigInt = function tryBigIntObject(value) {
+		try {
+			bigIntValueOf.call(value);
+			return true;
+		} catch (e) {
+		}
+		return false;
+	};
+
+	/** @type {import('.')} */
+	module.exports = function isBigInt(value) {
+		if (
+			value === null
+			|| typeof value === 'undefined'
+			|| typeof value === 'boolean'
+			|| typeof value === 'string'
+			|| typeof value === 'number'
+			|| typeof value === 'symbol'
+			|| typeof value === 'function'
+		) {
+			return false;
+		}
+		if (typeof value === 'bigint') {
+			return true;
+		}
+
+		return tryBigInt(value);
+	};
+} else {
+	/** @type {import('.')} */
+	module.exports = function isBigInt(value) {
+		return false && value;
+	};
+}