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/KeyForSymbol.js

@@ -0,0 +1,16 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var callBound = require('call-bound');
+
+var $keyFor = callBound('Symbol.keyFor', true);
+
+// https://262.ecma-international.org/14.0/#sec-keyforsymbol
+
+module.exports = function KeyForSymbol(sym) {
+	if (typeof sym !== 'symbol') {
+		throw new $TypeError('Assertion failed: `sym` must be a Symbol');
+	}
+	return $keyFor(sym);
+};