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/is-date-object/index.js

@@ -0,0 +1,27 @@
+'use strict';
+
+var callBound = require('call-bound');
+
+var getDay = callBound('Date.prototype.getDay');
+/** @type {import('.')} */
+var tryDateObject = function tryDateGetDayCall(value) {
+	try {
+		getDay(value);
+		return true;
+	} catch (e) {
+		return false;
+	}
+};
+
+/** @type {(value: unknown) => string} */
+var toStr = callBound('Object.prototype.toString');
+var dateClass = '[object Date]';
+var hasToStringTag = require('has-tostringtag/shams')();
+
+/** @type {import('.')} */
+module.exports = function isDateObject(value) {
+	if (typeof value !== 'object' || value === null) {
+		return false;
+	}
+	return hasToStringTag ? tryDateObject(value) : toStr(value) === dateClass;
+};