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/es-abstract/.editorconfig

@@ -0,0 +1,15 @@
+root = true
+
+[*]
+indent_style = tab;
+insert_final_newline = true;
+quote_type = auto;
+space_after_anonymous_functions = true;
+space_after_control_statements = true;
+spaces_around_operators = true;
+trim_trailing_whitespace = true;
+spaces_in_brackets = false;
+end_of_line = lf;
+
+[CHANGELOG.md]
+indent_style = space