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/2022/thisSymbolValue.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var $SyntaxError = require('es-errors/syntax');
+var callBound = require('call-bound');
+
+var $SymbolValueOf = callBound('Symbol.prototype.valueOf', true);
+
+// https://262.ecma-international.org/9.0/#sec-thissymbolvalue
+
+module.exports = function thisSymbolValue(value) {
+	if (typeof value === 'symbol') {
+		return value;
+	}
+
+	if (!$SymbolValueOf) {
+		throw new $SyntaxError('Symbols are not supported; thisSymbolValue requires that `value` be a Symbol or a Symbol object');
+	}
+
+	return $SymbolValueOf(value);
+};