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/PrecacheFallbackPlugin.d.ts

@@ -0,0 +1,42 @@
+import { WorkboxPlugin } from 'workbox-core/types.js';
+import { PrecacheController } from './PrecacheController.js';
+import './_version.js';
+/**
+ * `PrecacheFallbackPlugin` allows you to specify an "offline fallback"
+ * response to be used when a given strategy is unable to generate a response.
+ *
+ * It does this by intercepting the `handlerDidError` plugin callback
+ * and returning a precached response, taking the expected revision parameter
+ * into account automatically.
+ *
+ * Unless you explicitly pass in a `PrecacheController` instance to the
+ * constructor, the default instance will be used. Generally speaking, most
+ * developers will end up using the default.
+ *
+ * @memberof workbox-precaching
+ */
+declare class PrecacheFallbackPlugin implements WorkboxPlugin {
+    private readonly _fallbackURL;
+    private readonly _precacheController;
+    /**
+     * Constructs a new PrecacheFallbackPlugin with the associated fallbackURL.
+     *
+     * @param {Object} config
+     * @param {string} config.fallbackURL A precached URL to use as the fallback
+     *     if the associated strategy can't generate a response.
+     * @param {PrecacheController} [config.precacheController] An optional
+     *     PrecacheController instance. If not provided, the default
+     *     PrecacheController will be used.
+     */
+    constructor({ fallbackURL, precacheController, }: {
+        fallbackURL: string;
+        precacheController?: PrecacheController;
+    });
+    /**
+     * @return {Promise<Response>} The precache response for the fallback URL.
+     *
+     * @private
+     */
+    handlerDidError: WorkboxPlugin['handlerDidError'];
+}
+export { PrecacheFallbackPlugin };