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/nn.ts

@@ -0,0 +1,44 @@
+/** Norwegian Nynorsk strings. Ported from res/values-nn/strings.xml. */
+export const nn: Record<string, string> = {
+  app_name: 'Tilfluktsrom',
+
+  status_ready: 'Klar',
+  status_loading: 'Lastar tilfluktsromdata\u2026',
+  status_updating: 'Oppdaterer\u2026',
+  status_offline: 'Fr\u00e5kopla modus',
+  status_shelters_loaded: '%d tilfluktsrom lasta',
+  status_no_location: 'Ventar p\u00e5 GPS\u2026',
+  status_caching_map: 'Lagrar kart for fr\u00e5kopla bruk\u2026',
+
+  loading_shelters: 'Lastar ned tilfluktsromdata\u2026',
+  loading_map: 'Lagrar kartfliser\u2026',
+  loading_map_explanation:
+    'F\u00f8rebur fr\u00e5kopla kart.\nKartet vil rulle kort for \u00e5 lagre omgjevnadene dine.',
+  loading_first_time: 'Gjer klar for fyrste gongs bruk\u2026',
+
+  shelter_capacity: '%d plassar',
+  shelter_room_nr: 'Rom %d',
+  nearest_shelter: 'N\u00e6raste tilfluktsrom',
+  no_shelters: 'Ingen tilfluktsromdata tilgjengeleg',
+
+  action_refresh: 'Oppdater data',
+  action_toggle_view: 'Byt mellom kart og kompassvising',
+  action_skip: 'Hopp over',
+  action_cache_ok: 'Lagre kart',
+  action_cache_now: 'Lagre no',
+  warning_no_map_cache:
+    'Ingen fr\u00e5kopla kart lagra. Kartet krev internett.',
+
+  permission_location_title: 'Posisjonsløyve krevst',
+  permission_location_message:
+    'Denne appen treng posisjonen din for \u00e5 finne n\u00e6raste tilfluktsrom. Ver venleg og gje tilgang til posisjon.',
+  permission_denied:
+    'Posisjonsløyve avsl\u00e5tt. Appen kan ikkje finne tilfluktsrom i n\u00e6rleiken utan det.',
+
+  error_download_failed:
+    'Kunne ikkje laste ned tilfluktsromdata. Sjekk internettilkoplinga.',
+  error_no_data_offline:
+    'Ingen lagra data tilgjengeleg. Kopla til internett for \u00e5 laste ned tilfluktsromdata.',
+  update_success: 'Tilfluktsromdata oppdatert',
+  update_failed: 'Oppdatering mislukkast \u2014 brukar lagra data',
+};