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/es-abstract/2020/Number/sameValueZero.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var isNaN = require('../../helpers/isNaN');
+
+// https://262.ecma-international.org/11.0/#sec-numeric-types-number-sameValueZero
+
+module.exports = function NumberSameValueZero(x, y) {
+	if (typeof x !== 'number' || typeof y !== 'number') {
+		throw new $TypeError('Assertion failed: `x` and `y` arguments must be Numbers');
+	}
+
+	var xNaN = isNaN(x);
+	var yNaN = isNaN(y);
+	if (xNaN || yNaN) {
+		return xNaN === yNaN;
+	}
+	return x === y;
+};