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-precaching/cleanupOutdatedCaches.js

@@ -0,0 +1,32 @@
+/*
+  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 { cacheNames } from 'workbox-core/_private/cacheNames.js';
+import { logger } from 'workbox-core/_private/logger.js';
+import { deleteOutdatedCaches } from './utils/deleteOutdatedCaches.js';
+import './_version.js';
+/**
+ * Adds an `activate` event listener which will clean up incompatible
+ * precaches that were created by older versions of Workbox.
+ *
+ * @memberof workbox-precaching
+ */
+function cleanupOutdatedCaches() {
+    // See https://github.com/Microsoft/TypeScript/issues/28357#issuecomment-436484705
+    self.addEventListener('activate', ((event) => {
+        const cacheName = cacheNames.getPrecacheName();
+        event.waitUntil(deleteOutdatedCaches(cacheName).then((cachesDeleted) => {
+            if (process.env.NODE_ENV !== 'production') {
+                if (cachesDeleted.length > 0) {
+                    logger.log(`The following out-of-date precaches were cleaned up ` +
+                        `automatically:`, cachesDeleted);
+                }
+            }
+        }));
+    }));
+}
+export { cleanupOutdatedCaches };