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/vitest/dist/chunks/date.W2xKR2qe.js

@@ -0,0 +1,53 @@
+const RealDate = Date;
+let now = null;
+class MockDate extends RealDate {
+  constructor(y, m, d, h, M, s, ms) {
+    super();
+    let date;
+    switch (arguments.length) {
+      case 0:
+        if (now !== null) {
+          date = new RealDate(now.valueOf());
+        } else {
+          date = new RealDate();
+        }
+        break;
+      case 1:
+        date = new RealDate(y);
+        break;
+      default:
+        d = typeof d === "undefined" ? 1 : d;
+        h = h || 0;
+        M = M || 0;
+        s = s || 0;
+        ms = ms || 0;
+        date = new RealDate(y, m, d, h, M, s, ms);
+        break;
+    }
+    Object.setPrototypeOf(date, MockDate.prototype);
+    return date;
+  }
+}
+MockDate.UTC = RealDate.UTC;
+MockDate.now = function() {
+  return new MockDate().valueOf();
+};
+MockDate.parse = function(dateString) {
+  return RealDate.parse(dateString);
+};
+MockDate.toString = function() {
+  return RealDate.toString();
+};
+function mockDate(date) {
+  const dateObj = new RealDate(date.valueOf());
+  if (Number.isNaN(dateObj.getTime())) {
+    throw new TypeError(`mockdate: The time set is an invalid date: ${date}`);
+  }
+  globalThis.Date = MockDate;
+  now = dateObj.valueOf();
+}
+function resetDate() {
+  globalThis.Date = RealDate;
+}
+
+export { RealDate as R, mockDate as m, resetDate as r };