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/_baseXor.js

@@ -0,0 +1,36 @@
+var baseDifference = require('./_baseDifference'),
+    baseFlatten = require('./_baseFlatten'),
+    baseUniq = require('./_baseUniq');
+
+/**
+ * The base implementation of methods like `_.xor`, without support for
+ * iteratee shorthands, that accepts an array of arrays to inspect.
+ *
+ * @private
+ * @param {Array} arrays The arrays to inspect.
+ * @param {Function} [iteratee] The iteratee invoked per element.
+ * @param {Function} [comparator] The comparator invoked per element.
+ * @returns {Array} Returns the new array of values.
+ */
+function baseXor(arrays, iteratee, comparator) {
+  var length = arrays.length;
+  if (length < 2) {
+    return length ? baseUniq(arrays[0]) : [];
+  }
+  var index = -1,
+      result = Array(length);
+
+  while (++index < length) {
+    var array = arrays[index],
+        othIndex = -1;
+
+    while (++othIndex < length) {
+      if (othIndex != index) {
+        result[index] = baseDifference(result[index] || array, arrays[othIndex], iteratee, comparator);
+      }
+    }
+  }
+  return baseUniq(baseFlatten(result, 1), iteratee, comparator);
+}
+
+module.exports = baseXor;