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/index.js

@@ -0,0 +1,27 @@
+'use strict'
+
+module.exports = {
+  // Export promiseified graceful-fs:
+  ...require('./fs'),
+  // Export extra methods:
+  ...require('./copy-sync'),
+  ...require('./copy'),
+  ...require('./empty'),
+  ...require('./ensure'),
+  ...require('./json'),
+  ...require('./mkdirs'),
+  ...require('./move-sync'),
+  ...require('./move'),
+  ...require('./output'),
+  ...require('./path-exists'),
+  ...require('./remove')
+}
+
+// Export fs.promises as a getter property so that we don't trigger
+// ExperimentalWarning before fs.promises is actually accessed.
+const fs = require('fs')
+if (Object.getOwnPropertyDescriptor(fs, 'promises')) {
+  Object.defineProperty(module.exports, 'promises', {
+    get () { return fs.promises }
+  })
+}