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/lodash/xor.js

@@ -0,0 +1,28 @@
+var arrayFilter = require('./_arrayFilter'),
+    baseRest = require('./_baseRest'),
+    baseXor = require('./_baseXor'),
+    isArrayLikeObject = require('./isArrayLikeObject');
+
+/**
+ * Creates an array of unique values that is the
+ * [symmetric difference](https://en.wikipedia.org/wiki/Symmetric_difference)
+ * of the given arrays. The order of result values is determined by the order
+ * they occur in the arrays.
+ *
+ * @static
+ * @memberOf _
+ * @since 2.4.0
+ * @category Array
+ * @param {...Array} [arrays] The arrays to inspect.
+ * @returns {Array} Returns the new array of filtered values.
+ * @see _.difference, _.without
+ * @example
+ *
+ * _.xor([2, 1], [2, 3]);
+ * // => [1, 3]
+ */
+var xor = baseRest(function(arrays) {
+  return baseXor(arrayFilter(arrays, isArrayLikeObject));
+});
+
+module.exports = xor;