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/which-collection/index.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var isMap = require('is-map');
+var isSet = require('is-set');
+var isWeakMap = require('is-weakmap');
+var isWeakSet = require('is-weakset');
+
+/** @type {import('.')} */
+module.exports = function whichCollection(/** @type {unknown} */ value) {
+	if (value && typeof value === 'object') {
+		if (isMap(value)) {
+			return 'Map';
+		}
+		if (isSet(value)) {
+			return 'Set';
+		}
+		if (isWeakMap(value)) {
+			return 'WeakMap';
+		}
+		if (isWeakSet(value)) {
+			return 'WeakSet';
+		}
+	}
+	return false;
+};