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/_toKey.js

@@ -0,0 +1,21 @@
+var isSymbol = require('./isSymbol');
+
+/** Used as references for various `Number` constants. */
+var INFINITY = 1 / 0;
+
+/**
+ * Converts `value` to a string key if it's not a string or symbol.
+ *
+ * @private
+ * @param {*} value The value to inspect.
+ * @returns {string|symbol} Returns the key.
+ */
+function toKey(value) {
+  if (typeof value == 'string' || isSymbol(value)) {
+    return value;
+  }
+  var result = (value + '');
+  return (result == '0' && (1 / value) == -INFINITY) ? '-0' : result;
+}
+
+module.exports = toKey;