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/2022/SameValue.js

@@ -0,0 +1,13 @@
+'use strict';
+
+var $isNaN = require('math-intrinsics/isNaN');
+
+// http://262.ecma-international.org/5.1/#sec-9.12
+
+module.exports = function SameValue(x, y) {
+	if (x === y) { // 0 === -0, but they are not identical.
+		if (x === 0) { return 1 / x === 1 / y; }
+		return true;
+	}
+	return $isNaN(x) && $isNaN(y);
+};