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/workbox-window/utils/urlsMatch.js

@@ -0,0 +1,21 @@
+/*
+  Copyright 2019 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+import '../_version.js';
+/**
+ * Returns true if two URLs have the same `.href` property. The URLS can be
+ * relative, and if they are the current location href is used to resolve URLs.
+ *
+ * @private
+ * @param {string} url1
+ * @param {string} url2
+ * @return {boolean}
+ */
+export function urlsMatch(url1, url2) {
+    const { href } = location;
+    return new URL(url1, href).href === new URL(url2, href).href;
+}