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/2023/IsDetachedBuffer.js

@@ -0,0 +1,28 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var $byteLength = require('array-buffer-byte-length');
+var availableTypedArrays = require('available-typed-arrays')();
+var callBound = require('call-bound');
+var isArrayBuffer = require('is-array-buffer');
+var isSharedArrayBuffer = require('is-shared-array-buffer');
+
+var $sabByteLength = callBound('SharedArrayBuffer.prototype.byteLength', true);
+
+// https://262.ecma-international.org/8.0/#sec-isdetachedbuffer
+
+module.exports = function IsDetachedBuffer(arrayBuffer) {
+	var isSAB = isSharedArrayBuffer(arrayBuffer);
+	if (!isArrayBuffer(arrayBuffer) && !isSAB) {
+		throw new $TypeError('Assertion failed: `arrayBuffer` must be an Object with an [[ArrayBufferData]] internal slot');
+	}
+	if ((isSAB ? $sabByteLength : $byteLength)(arrayBuffer) === 0) {
+		try {
+			new global[availableTypedArrays[0]](arrayBuffer); // eslint-disable-line no-new
+		} catch (error) {
+			return !!error && error.name === 'TypeError';
+		}
+	}
+	return false;
+};