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/vite-plugin-pwa/vanillajs.d.ts

@@ -0,0 +1,13 @@
+declare module 'virtual:pwa-register' {
+  import type { RegisterSWOptions } from 'vite-plugin-pwa/types'
+
+  export type { RegisterSWOptions }
+
+  /**
+   * Registers the service worker returning a callback to reload the current page when an update is found.
+   *
+   * @param options the options to register the service worker.
+   * @return (reloadPage?: boolean) => Promise<void> From version 0.13.2+ `reloadPage` param is not used anymore.
+   */
+  export function registerSW(options?: RegisterSWOptions): (reloadPage?: boolean) => Promise<void>
+}