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/offlineFallback.js

@@ -0,0 +1,59 @@
+/*
+  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 { setCatchHandler } from 'workbox-routing/setCatchHandler.js';
+import { matchPrecache } from 'workbox-precaching/matchPrecache.js';
+import './_version.js';
+/**
+ * An implementation of the [comprehensive fallbacks recipe]{@link https://developers.google.com/web/tools/workbox/guides/advanced-recipes#comprehensive_fallbacks}. Be sure to include the fallbacks in your precache injection
+ *
+ * @memberof workbox-recipes
+ *
+ * @param {Object} [options]
+ * @param {string} [options.pageFallback] Precache name to match for pag fallbacks. Defaults to offline.html
+ * @param {string} [options.imageFallback] Precache name to match for image fallbacks.
+ * @param {string} [options.fontFallback] Precache name to match for font fallbacks.
+ */
+function offlineFallback(options = {}) {
+    const pageFallback = options.pageFallback || 'offline.html';
+    const imageFallback = options.imageFallback || false;
+    const fontFallback = options.fontFallback || false;
+    self.addEventListener('install', (event) => {
+        const files = [pageFallback];
+        if (imageFallback) {
+            files.push(imageFallback);
+        }
+        if (fontFallback) {
+            files.push(fontFallback);
+        }
+        event.waitUntil(self.caches
+            .open('workbox-offline-fallbacks')
+            .then((cache) => cache.addAll(files)));
+    });
+    const handler = async (options) => {
+        const dest = options.request.destination;
+        const cache = await self.caches.open('workbox-offline-fallbacks');
+        if (dest === 'document') {
+            const match = (await matchPrecache(pageFallback)) ||
+                (await cache.match(pageFallback));
+            return match || Response.error();
+        }
+        if (dest === 'image' && imageFallback !== false) {
+            const match = (await matchPrecache(imageFallback)) ||
+                (await cache.match(imageFallback));
+            return match || Response.error();
+        }
+        if (dest === 'font' && fontFallback !== false) {
+            const match = (await matchPrecache(fontFallback)) ||
+                (await cache.match(fontFallback));
+            return match || Response.error();
+        }
+        return Response.error();
+    };
+    setCatchHandler(handler);
+}
+export { offlineFallback };