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/globalthis/shim.js

@@ -0,0 +1,29 @@
+'use strict';
+
+var define = require('define-properties');
+var gOPD = require('gopd');
+var getPolyfill = require('./polyfill');
+
+module.exports = function shimGlobal() {
+	var polyfill = getPolyfill();
+	if (define.supportsDescriptors) {
+		var descriptor = gOPD(polyfill, 'globalThis');
+		if (
+			!descriptor
+			|| (
+				descriptor.configurable
+				&& (descriptor.enumerable || !descriptor.writable || globalThis !== polyfill)
+			)
+		) {
+			Object.defineProperty(polyfill, 'globalThis', {
+				configurable: true,
+				enumerable: false,
+				value: polyfill,
+				writable: true
+			});
+		}
+	} else if (typeof globalThis !== 'object' || globalThis !== polyfill) {
+		polyfill.globalThis = polyfill;
+	}
+	return polyfill;
+};