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/leaflet.offline/changelog.md

@@ -0,0 +1,10 @@
+# Version 3
+
+- Removal of setOption method on the control
+- getTile is now getBlobByKey
+- openTilesDataBase is now an export function to get whole idb database
+- New control option alwaysDownload, if false, the control will not redownload tiles already in the db (and the savetile\* event do not fire)
+
+# Version 4
+
+- Changed arguments of getStoredTilesAsJson: send an object with tilesize instead of the full layer