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/2017/UTF16Decode.js

@@ -0,0 +1,21 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $TypeError = require('es-errors/type');
+var $fromCharCode = GetIntrinsic('%String.fromCharCode%');
+
+// https://262.ecma-international.org/7.0/#sec-utf16decode
+
+var isLeadingSurrogate = require('../helpers/isLeadingSurrogate');
+var isTrailingSurrogate = require('../helpers/isTrailingSurrogate');
+
+// https://262.ecma-international.org/11.0/#sec-utf16decodesurrogatepair
+
+module.exports = function UTF16Decode(lead, trail) {
+	if (!isLeadingSurrogate(lead) || !isTrailingSurrogate(trail)) {
+		throw new $TypeError('Assertion failed: `lead` must be a leading surrogate char code, and `trail` must be a trailing surrogate char code');
+	}
+	// var cp = (lead - 0xD800) * 0x400 + (trail - 0xDC00) + 0x10000;
+	return $fromCharCode(lead) + $fromCharCode(trail);
+};