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/awaitify.js

@@ -0,0 +1,28 @@
+'use strict';
+
+Object.defineProperty(exports, "__esModule", {
+    value: true
+});
+exports.default = awaitify;
+// conditionally promisify a function.
+// only return a promise if a callback is omitted
+function awaitify(asyncFn, arity) {
+    if (!arity) arity = asyncFn.length;
+    if (!arity) throw new Error('arity is undefined');
+    function awaitable(...args) {
+        if (typeof args[arity - 1] === 'function') {
+            return asyncFn.apply(this, args);
+        }
+
+        return new Promise((resolve, reject) => {
+            args[arity - 1] = (err, ...cbArgs) => {
+                if (err) return reject(err);
+                resolve(cbArgs.length > 1 ? cbArgs : cbArgs[0]);
+            };
+            asyncFn.apply(this, args);
+        });
+    }
+
+    return awaitable;
+}
+module.exports = exports.default;