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/_isIndex.js

@@ -0,0 +1,25 @@
+/** Used as references for various `Number` constants. */
+var MAX_SAFE_INTEGER = 9007199254740991;
+
+/** Used to detect unsigned integer values. */
+var reIsUint = /^(?:0|[1-9]\d*)$/;
+
+/**
+ * Checks if `value` is a valid array-like index.
+ *
+ * @private
+ * @param {*} value The value to check.
+ * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
+ * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
+ */
+function isIndex(value, length) {
+  var type = typeof value;
+  length = length == null ? MAX_SAFE_INTEGER : length;
+
+  return !!length &&
+    (type == 'number' ||
+      (type != 'symbol' && reIsUint.test(value))) &&
+        (value > -1 && value % 1 == 0 && value < length);
+}
+
+module.exports = isIndex;