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/_setToPairs.js

@@ -0,0 +1,18 @@
+/**
+ * Converts `set` to its value-value pairs.
+ *
+ * @private
+ * @param {Object} set The set to convert.
+ * @returns {Array} Returns the value-value pairs.
+ */
+function setToPairs(set) {
+  var index = -1,
+      result = Array(set.size);
+
+  set.forEach(function(value) {
+    result[++index] = [value, value];
+  });
+  return result;
+}
+
+module.exports = setToPairs;