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/src/i18n/en.ts

@@ -0,0 +1,49 @@
+/** English strings — default locale. Ported from res/values/strings.xml. */
+export const en: Record<string, string> = {
+  app_name: 'Tilfluktsrom',
+
+  // Status
+  status_ready: 'Ready',
+  status_loading: 'Loading shelter data\u2026',
+  status_updating: 'Updating\u2026',
+  status_offline: 'Offline mode',
+  status_shelters_loaded: '%d shelters loaded',
+  status_no_location: 'Waiting for GPS\u2026',
+  status_caching_map: 'Caching map for offline use\u2026',
+
+  // Loading
+  loading_shelters: 'Downloading shelter data\u2026',
+  loading_map: 'Caching map tiles\u2026',
+  loading_map_explanation:
+    'Preparing offline map.\nThe map will scroll briefly to cache your surroundings.',
+  loading_first_time: 'Setting up for first use\u2026',
+
+  // Shelter info
+  shelter_capacity: '%d places',
+  shelter_room_nr: 'Room %d',
+  nearest_shelter: 'Nearest shelter',
+  no_shelters: 'No shelter data available',
+
+  // Actions
+  action_refresh: 'Refresh data',
+  action_toggle_view: 'Toggle map/compass view',
+  action_skip: 'Skip',
+  action_cache_ok: 'Cache map',
+  action_cache_now: 'Cache now',
+  warning_no_map_cache: 'No offline map cached. Map requires internet.',
+
+  // Permissions
+  permission_location_title: 'Location permission required',
+  permission_location_message:
+    'This app needs your location to find the nearest shelter. Please grant location access.',
+  permission_denied:
+    'Location permission denied. The app cannot find nearby shelters without it.',
+
+  // Errors
+  error_download_failed:
+    'Could not download shelter data. Check your internet connection.',
+  error_no_data_offline:
+    'No cached data available. Connect to the internet to download shelter data.',
+  update_success: 'Shelter data updated',
+  update_failed: 'Update failed \u2014 using cached data',
+};