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/vitest/index.cjs

@@ -0,0 +1,5 @@
+throw new Error(
+  'Vitest cannot be imported in a CommonJS module using require(). Please use "import" instead.'
+  + '\n\nIf you are using "import" in your source code, then it\'s possible it was bundled into require() automatically by your bundler. '
+  + 'In that case, do not bundle CommonJS output since it will never work with Vitest, or use dynamic import() which is available in all CommonJS modules.',
+)