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/ensure/index.js

@@ -0,0 +1,23 @@
+'use strict'
+
+const file = require('./file')
+const link = require('./link')
+const symlink = require('./symlink')
+
+module.exports = {
+  // file
+  createFile: file.createFile,
+  createFileSync: file.createFileSync,
+  ensureFile: file.createFile,
+  ensureFileSync: file.createFileSync,
+  // link
+  createLink: link.createLink,
+  createLinkSync: link.createLinkSync,
+  ensureLink: link.createLink,
+  ensureLinkSync: link.createLinkSync,
+  // symlink
+  createSymlink: symlink.createSymlink,
+  createSymlinkSync: symlink.createSymlinkSync,
+  ensureSymlink: symlink.createSymlink,
+  ensureSymlinkSync: symlink.createSymlinkSync
+}