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/_baseFlatten.js

@@ -0,0 +1,38 @@
+var arrayPush = require('./_arrayPush'),
+    isFlattenable = require('./_isFlattenable');
+
+/**
+ * The base implementation of `_.flatten` with support for restricting flattening.
+ *
+ * @private
+ * @param {Array} array The array to flatten.
+ * @param {number} depth The maximum recursion depth.
+ * @param {boolean} [predicate=isFlattenable] The function invoked per iteration.
+ * @param {boolean} [isStrict] Restrict to values that pass `predicate` checks.
+ * @param {Array} [result=[]] The initial result value.
+ * @returns {Array} Returns the new flattened array.
+ */
+function baseFlatten(array, depth, predicate, isStrict, result) {
+  var index = -1,
+      length = array.length;
+
+  predicate || (predicate = isFlattenable);
+  result || (result = []);
+
+  while (++index < length) {
+    var value = array[index];
+    if (depth > 0 && predicate(value)) {
+      if (depth > 1) {
+        // Recursively flatten arrays (susceptible to call stack limits).
+        baseFlatten(value, depth - 1, predicate, isStrict, result);
+      } else {
+        arrayPush(result, value);
+      }
+    } else if (!isStrict) {
+      result[result.length] = value;
+    }
+  }
+  return result;
+}
+
+module.exports = baseFlatten;