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/has-proto/accessor.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var result = require('./')();
+
+var test = {
+	__proto__: null,
+	foo: {}
+};
+
+/** @type {import('./accessor')} */
+module.exports = function hasAccessor() {
+	/* eslint no-proto: 0 */
+	return result
+		&& !('toString' in test)
+		// eslint-disable-next-line no-extra-parens
+		&& /** @type {{ __proto__?: typeof Object.prototype }} */ ({}).__proto__ === Object.prototype
+		// eslint-disable-next-line no-extra-parens
+		&& /** @type {ReadonlyArray<never> & { __proto__?: typeof Array.prototype }} */ (
+			[]).__proto__ === Array.prototype;
+};