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/2025/IsStringWellFormedUnicode.js

@@ -0,0 +1,23 @@
+'use strict';
+
+var CodePointAt = require('./CodePointAt');
+
+var $TypeError = require('es-errors/type');
+
+// https://262.ecma-international.org/14.0/#sec-isstringwellformedunicode
+
+module.exports = function IsStringWellFormedUnicode(string) {
+	if (typeof string !== 'string') {
+		throw new $TypeError('Assertion failed: `string` must be a String');
+	}
+	var len = string.length; // step 1
+	var k = 0; // step 2
+	while (k < len) { // step 3
+		var cp = CodePointAt(string, k); // step 3.a
+		if (cp['[[IsUnpairedSurrogate]]']) {
+			return false; // step 3.b
+		}
+		k += cp['[[CodeUnitCount]]']; // step 3.c
+	}
+	return true; // step 4
+};