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/2021/Number/exponentiate.js

@@ -0,0 +1,74 @@
+'use strict';
+
+// var isNegativeZero = require('math-intrinsics/isNegativeZero');
+var $pow = require('math-intrinsics/pow');
+
+var $TypeError = require('es-errors/type');
+
+/*
+var abs = require('math-intrinsics/abs');
+var isFinite = require('math-intrinsics/isFinite');
+var isNaN = require('math-intrinsics/isNaN');
+
+var IsInteger = require('math-intrinsics/isInteger');
+*/
+
+// https://262.ecma-international.org/11.0/#sec-numeric-types-number-exponentiate
+
+/* eslint max-lines-per-function: 0, max-statements: 0 */
+
+module.exports = function NumberExponentiate(base, exponent) {
+	if (typeof base !== 'number' || typeof exponent !== 'number') {
+		throw new $TypeError('Assertion failed: `base` and `exponent` arguments must be Numbers');
+	}
+	return $pow(base, exponent);
+	/*
+	if (isNaN(exponent)) {
+		return NaN;
+	}
+	if (exponent === 0) {
+		return 1;
+	}
+	if (isNaN(base)) {
+		return NaN;
+	}
+	var aB = abs(base);
+	if (aB > 1 && exponent === Infinity) {
+		return Infinity;
+	}
+	if (aB > 1 && exponent === -Infinity) {
+		return 0;
+	}
+	if (aB === 1 && (exponent === Infinity || exponent === -Infinity)) {
+		return NaN;
+	}
+	if (aB < 1 && exponent === Infinity) {
+		return +0;
+	}
+	if (aB < 1 && exponent === -Infinity) {
+		return Infinity;
+	}
+	if (base === Infinity) {
+		return exponent > 0 ? Infinity : 0;
+	}
+	if (base === -Infinity) {
+		var isOdd = true;
+		if (exponent > 0) {
+			return isOdd ? -Infinity : Infinity;
+		}
+		return isOdd ? -0 : 0;
+	}
+	if (exponent > 0) {
+		return isNegativeZero(base) ? Infinity : 0;
+	}
+	if (isNegativeZero(base)) {
+		if (exponent > 0) {
+			return isOdd ? -0 : 0;
+		}
+		return isOdd ? -Infinity : Infinity;
+	}
+	if (base < 0 && isFinite(base) && isFinite(exponent) && !IsInteger(exponent)) {
+		return NaN;
+	}
+	*/
+};