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/_baseNth.js

@@ -0,0 +1,20 @@
+var isIndex = require('./_isIndex');
+
+/**
+ * The base implementation of `_.nth` which doesn't coerce arguments.
+ *
+ * @private
+ * @param {Array} array The array to query.
+ * @param {number} n The index of the element to return.
+ * @returns {*} Returns the nth element of `array`.
+ */
+function baseNth(array, n) {
+  var length = array.length;
+  if (!length) {
+    return;
+  }
+  n += n < 0 ? length : 0;
+  return isIndex(n, length) ? array[n] : undefined;
+}
+
+module.exports = baseNth;