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/safe-array-concat/index.js

@@ -0,0 +1,43 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+var $concat = GetIntrinsic('%Array.prototype.concat%');
+
+var callBind = require('call-bind');
+
+var callBound = require('call-bound');
+var $slice = callBound('Array.prototype.slice');
+
+var hasSymbols = require('has-symbols/shams')();
+var isConcatSpreadable = hasSymbols && Symbol.isConcatSpreadable;
+
+/** @type {never[]} */ var empty = [];
+var $concatApply = isConcatSpreadable ? callBind.apply($concat, empty) : null;
+
+// eslint-disable-next-line no-extra-parens
+var isArray = isConcatSpreadable ? /** @type {(value: unknown) => value is unknown[]} */ (require('isarray')) : null;
+
+/** @type {import('.')} */
+module.exports = isConcatSpreadable
+	// eslint-disable-next-line no-unused-vars
+	? function safeArrayConcat(item) {
+		for (var i = 0; i < arguments.length; i += 1) {
+			/** @type {typeof item} */ var arg = arguments[i];
+			// @ts-expect-error ts(2538) see https://github.com/microsoft/TypeScript/issues/9998#issuecomment-1890787975; works if `const`
+			if (arg && typeof arg === 'object' && typeof arg[isConcatSpreadable] === 'boolean') {
+				// @ts-expect-error ts(7015) TS doesn't yet support Symbol indexing
+				if (!empty[isConcatSpreadable]) {
+					// @ts-expect-error ts(7015) TS doesn't yet support Symbol indexing
+					empty[isConcatSpreadable] = true;
+				}
+				// @ts-expect-error ts(2721) ts(18047) not sure why TS can't figure out this can't be null
+				var arr = isArray(arg) ? $slice(arg) : [arg];
+				// @ts-expect-error ts(7015) TS can't handle expandos on an array
+				arr[isConcatSpreadable] = true; // shadow the property. TODO: use [[Define]]
+				arguments[i] = arr;
+			}
+		}
+		// @ts-expect-error ts(2345) https://github.com/microsoft/TypeScript/issues/57164 TS doesn't understand that apply can take an arguments object
+		return $concatApply(arguments);
+	}
+	: callBind($concat, empty);