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-cacheable-response/CacheableResponsePlugin.js

@@ -0,0 +1,48 @@
+/*
+  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 { CacheableResponse, } from './CacheableResponse.js';
+import './_version.js';
+/**
+ * A class implementing the `cacheWillUpdate` lifecycle callback. This makes it
+ * easier to add in cacheability checks to requests made via Workbox's built-in
+ * strategies.
+ *
+ * @memberof workbox-cacheable-response
+ */
+class CacheableResponsePlugin {
+    /**
+     * To construct a new CacheableResponsePlugin instance you must provide at
+     * least one of the `config` properties.
+     *
+     * If both `statuses` and `headers` are specified, then both conditions must
+     * be met for the `Response` to be considered cacheable.
+     *
+     * @param {Object} config
+     * @param {Array<number>} [config.statuses] One or more status codes that a
+     * `Response` can have and be considered cacheable.
+     * @param {Object<string,string>} [config.headers] A mapping of header names
+     * and expected values that a `Response` can have and be considered cacheable.
+     * If multiple headers are provided, only one needs to be present.
+     */
+    constructor(config) {
+        /**
+         * @param {Object} options
+         * @param {Response} options.response
+         * @return {Response|null}
+         * @private
+         */
+        this.cacheWillUpdate = async ({ response }) => {
+            if (this._cacheableResponse.isResponseCacheable(response)) {
+                return response;
+            }
+            return null;
+        };
+        this._cacheableResponse = new CacheableResponse(config);
+    }
+}
+export { CacheableResponsePlugin };