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/jsonpointer/jsonpointer.d.ts

@@ -0,0 +1,35 @@
+interface JSONPointer {
+    /**
+     * Looks up a JSON pointer in an object
+     */
+    get(object: Object): any;
+
+
+    /**
+     * Set a value for a JSON pointer on object
+     */
+    set(object: Object, value: any): void;
+}
+
+
+declare namespace JSONPointer {
+    /**
+     * Looks up a JSON pointer in an object
+     */
+    function get(object: Object, pointer: string): any;
+
+
+    /**
+     * Set a value for a JSON pointer on object
+     */
+    function set(object: Object, pointer: string, value: any): void;
+
+
+    /**
+     *  Builds a JSONPointer instance from a pointer value.
+     */
+    function compile(pointer: string): JSONPointer;
+}
+
+
+export = JSONPointer;