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-recipes/pageCache.js

@@ -0,0 +1,46 @@
+/*
+  Copyright 2020 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 { warmStrategyCache } from './warmStrategyCache';
+import { registerRoute } from 'workbox-routing/registerRoute.js';
+import { NetworkFirst } from 'workbox-strategies/NetworkFirst.js';
+import { CacheableResponsePlugin } from 'workbox-cacheable-response/CacheableResponsePlugin.js';
+import './_version.js';
+/**
+ * An implementation of a page caching recipe with a network timeout
+ *
+ * @memberof workbox-recipes
+ *
+ * @param {Object} [options]
+ * @param {string} [options.cacheName] Name for cache. Defaults to pages
+ * @param {RouteMatchCallback} [options.matchCallback] Workbox callback function to call to match to. Defaults to request.mode === 'navigate';
+ * @param {number} [options.networkTimoutSeconds] Maximum amount of time, in seconds, to wait on the network before falling back to cache. Defaults to 3
+ * @param {WorkboxPlugin[]} [options.plugins] Additional plugins to use for this recipe
+ * @param {string[]} [options.warmCache] Paths to call to use to warm this cache
+ */
+function pageCache(options = {}) {
+    const defaultMatchCallback = ({ request }) => request.mode === 'navigate';
+    const cacheName = options.cacheName || 'pages';
+    const matchCallback = options.matchCallback || defaultMatchCallback;
+    const networkTimeoutSeconds = options.networkTimeoutSeconds || 3;
+    const plugins = options.plugins || [];
+    plugins.push(new CacheableResponsePlugin({
+        statuses: [0, 200],
+    }));
+    const strategy = new NetworkFirst({
+        networkTimeoutSeconds,
+        cacheName,
+        plugins,
+    });
+    // Registers the route
+    registerRoute(matchCallback, strategy);
+    // Warms the cache
+    if (options.warmCache) {
+        warmStrategyCache({ urls: options.warmCache, strategy });
+    }
+}
+export { pageCache };