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/ToLength.js

@@ -0,0 +1,14 @@
+'use strict';
+
+var MAX_SAFE_INTEGER = require('math-intrinsics/constants/maxSafeInteger');
+
+var ToIntegerOrInfinity = require('./ToIntegerOrInfinity');
+
+// https://262.ecma-international.org/12.0/#sec-tolength
+
+module.exports = function ToLength(argument) {
+	var len = ToIntegerOrInfinity(argument);
+	if (len <= 0) { return 0; } // includes converting -0 to +0
+	if (len > MAX_SAFE_INTEGER) { return MAX_SAFE_INTEGER; }
+	return len;
+};