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/ArrayBufferByteLength.js

@@ -0,0 +1,41 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+// https://262.ecma-international.org/15.0/#sec-arraybufferbytelength
+
+var IsDetachedBuffer = require('./IsDetachedBuffer');
+
+var isArrayBuffer = require('is-array-buffer');
+var isSharedArrayBuffer = require('is-shared-array-buffer');
+var arrayBufferByteLength = require('array-buffer-byte-length');
+
+var callBound = require('call-bound');
+var $sabByteLength = callBound('SharedArrayBuffer.prototype.byteLength', true);
+
+var isGrowable = false; // TODO: support this
+
+module.exports = function ArrayBufferByteLength(arrayBuffer, order) {
+	var isSAB = isSharedArrayBuffer(arrayBuffer);
+	if (!isArrayBuffer(arrayBuffer) && !isSAB) {
+		throw new $TypeError('Assertion failed: `arrayBuffer` must be an ArrayBuffer or a SharedArrayBuffer');
+	}
+	if (order !== 'SEQ-CST' && order !== 'UNORDERED') {
+		throw new $TypeError('Assertion failed: `order` must be ~SEQ-CST~ or ~UNORDERED~');
+	}
+
+	// 1. If IsSharedArrayBuffer(arrayBuffer) is true and arrayBuffer has an [[ArrayBufferByteLengthData]] internal slot, then
+	// TODO: see if IsFixedLengthArrayBuffer can be used here in the spec instead
+	if (isSAB && isGrowable) { // step 1
+		// a. Let bufferByteLengthBlock be arrayBuffer.[[ArrayBufferByteLengthData]].
+		// b. Let rawLength be GetRawBytesFromSharedBlock(bufferByteLengthBlock, 0, BIGUINT64, true, order).
+		// c. Let isLittleEndian be the value of the [[LittleEndian]] field of the surrounding agent's Agent Record.
+		// d. Return ℝ(RawBytesToNumeric(BIGUINT64, rawLength, isLittleEndian)).
+	}
+
+	if (IsDetachedBuffer(arrayBuffer)) {
+		throw new $TypeError('Assertion failed: `arrayBuffer` must not be detached'); // step 2
+	}
+
+	return isSAB ? $sabByteLength(arrayBuffer) : arrayBufferByteLength(arrayBuffer);
+};