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/object.assign/polyfill.js

@@ -0,0 +1,55 @@
+'use strict';
+
+var implementation = require('./implementation');
+
+var lacksProperEnumerationOrder = function () {
+	if (!Object.assign) {
+		return false;
+	}
+	/*
+	 * v8, specifically in node 4.x, has a bug with incorrect property enumeration order
+	 * note: this does not detect the bug unless there's 20 characters
+	 */
+	var str = 'abcdefghijklmnopqrst';
+	var letters = str.split('');
+	var map = {};
+	for (var i = 0; i < letters.length; ++i) {
+		map[letters[i]] = letters[i];
+	}
+	var obj = Object.assign({}, map);
+	var actual = '';
+	for (var k in obj) {
+		actual += k;
+	}
+	return str !== actual;
+};
+
+var assignHasPendingExceptions = function () {
+	if (!Object.assign || !Object.preventExtensions) {
+		return false;
+	}
+	/*
+	 * Firefox 37 still has "pending exception" logic in its Object.assign implementation,
+	 * which is 72% slower than our shim, and Firefox 40's native implementation.
+	 */
+	var thrower = Object.preventExtensions({ 1: 2 });
+	try {
+		Object.assign(thrower, 'xy');
+	} catch (e) {
+		return thrower[1] === 'y';
+	}
+	return false;
+};
+
+module.exports = function getPolyfill() {
+	if (!Object.assign) {
+		return implementation;
+	}
+	if (lacksProperEnumerationOrder()) {
+		return implementation;
+	}
+	if (assignHasPendingExceptions()) {
+		return implementation;
+	}
+	return Object.assign;
+};