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/fs-extra/lib/json/jsonfile.js

@@ -0,0 +1,11 @@
+'use strict'
+
+const jsonFile = require('jsonfile')
+
+module.exports = {
+  // jsonfile exports
+  readJson: jsonFile.readFile,
+  readJsonSync: jsonFile.readFileSync,
+  writeJson: jsonFile.writeFile,
+  writeJsonSync: jsonFile.writeFileSync
+}