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/@babel/runtime/helpers/extends.js

@@ -0,0 +1,10 @@
+function _extends() {
+  return module.exports = _extends = Object.assign ? Object.assign.bind() : function (n) {
+    for (var e = 1; e < arguments.length; e++) {
+      var t = arguments[e];
+      for (var r in t) ({}).hasOwnProperty.call(t, r) && (n[r] = t[r]);
+    }
+    return n;
+  }, module.exports.__esModule = true, module.exports["default"] = module.exports, _extends.apply(null, arguments);
+}
+module.exports = _extends, module.exports.__esModule = true, module.exports["default"] = module.exports;