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/imageCache.js

@@ -0,0 +1,51 @@
+/*
+  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 { CacheFirst } from 'workbox-strategies/CacheFirst.js';
+import { CacheableResponsePlugin } from 'workbox-cacheable-response/CacheableResponsePlugin.js';
+import { ExpirationPlugin } from 'workbox-expiration/ExpirationPlugin.js';
+import './_version.js';
+/**
+ * An implementation of the [image caching recipe]{@link https://developers.google.com/web/tools/workbox/guides/common-recipes#caching_images}
+ *
+ * @memberof workbox-recipes
+ *
+ * @param {Object} [options]
+ * @param {string} [options.cacheName] Name for cache. Defaults to images
+ * @param {RouteMatchCallback} [options.matchCallback] Workbox callback function to call to match to. Defaults to request.destination === 'image';
+ * @param {number} [options.maxAgeSeconds] Maximum age, in seconds, that font entries will be cached for. Defaults to 30 days
+ * @param {number} [options.maxEntries] Maximum number of images that will be cached. Defaults to 60
+ * @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 imageCache(options = {}) {
+    const defaultMatchCallback = ({ request }) => request.destination === 'image';
+    const cacheName = options.cacheName || 'images';
+    const matchCallback = options.matchCallback || defaultMatchCallback;
+    const maxAgeSeconds = options.maxAgeSeconds || 30 * 24 * 60 * 60;
+    const maxEntries = options.maxEntries || 60;
+    const plugins = options.plugins || [];
+    plugins.push(new CacheableResponsePlugin({
+        statuses: [0, 200],
+    }));
+    plugins.push(new ExpirationPlugin({
+        maxEntries,
+        maxAgeSeconds,
+    }));
+    const strategy = new CacheFirst({
+        cacheName,
+        plugins,
+    });
+    registerRoute(matchCallback, strategy);
+    // Warms the cache
+    if (options.warmCache) {
+        warmStrategyCache({ urls: options.warmCache, strategy });
+    }
+}
+export { imageCache };