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-navigation-preload/enable.js

@@ -0,0 +1,41 @@
+/*
+  Copyright 2018 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 { logger } from 'workbox-core/_private/logger.js';
+import { isSupported } from './isSupported.js';
+import './_version.js';
+/**
+ * If the browser supports Navigation Preload, then this will enable it.
+ *
+ * @param {string} [headerValue] Optionally, allows developers to
+ * [override](https://developers.google.com/web/updates/2017/02/navigation-preload#changing_the_header)
+ * the value of the `Service-Worker-Navigation-Preload` header which will be
+ * sent to the server when making the navigation request.
+ *
+ * @memberof workbox-navigation-preload
+ */
+function enable(headerValue) {
+    if (isSupported()) {
+        self.addEventListener('activate', (event) => {
+            event.waitUntil(self.registration.navigationPreload.enable().then(() => {
+                // Defaults to Service-Worker-Navigation-Preload: true if not set.
+                if (headerValue) {
+                    void self.registration.navigationPreload.setHeaderValue(headerValue);
+                }
+                if (process.env.NODE_ENV !== 'production') {
+                    logger.log(`Navigation preload is enabled.`);
+                }
+            }));
+        });
+    }
+    else {
+        if (process.env.NODE_ENV !== 'production') {
+            logger.log(`Navigation preload is not supported in this browser.`);
+        }
+    }
+}
+export { enable };