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/async/internal/setImmediate.js

@@ -0,0 +1,34 @@
+'use strict';
+
+Object.defineProperty(exports, "__esModule", {
+    value: true
+});
+exports.fallback = fallback;
+exports.wrap = wrap;
+/* istanbul ignore file */
+
+var hasQueueMicrotask = exports.hasQueueMicrotask = typeof queueMicrotask === 'function' && queueMicrotask;
+var hasSetImmediate = exports.hasSetImmediate = typeof setImmediate === 'function' && setImmediate;
+var hasNextTick = exports.hasNextTick = typeof process === 'object' && typeof process.nextTick === 'function';
+
+function fallback(fn) {
+    setTimeout(fn, 0);
+}
+
+function wrap(defer) {
+    return (fn, ...args) => defer(() => fn(...args));
+}
+
+var _defer;
+
+if (hasQueueMicrotask) {
+    _defer = queueMicrotask;
+} else if (hasSetImmediate) {
+    _defer = setImmediate;
+} else if (hasNextTick) {
+    _defer = process.nextTick;
+} else {
+    _defer = fallback;
+}
+
+exports.default = wrap(_defer);