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/safe-push-apply/index.js

@@ -0,0 +1,15 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var isArray = require('isarray');
+
+/** @type {import('.')} */
+module.exports = function safePushApply(target, source) {
+	if (!isArray(target)) {
+		throw new $TypeError('target must be an array');
+	}
+	for (var i = 0; i < source.length; i++) {
+		target[target.length] = source[i]; // eslint-disable-line no-param-reassign
+	}
+};