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/mkdirs/index.js

@@ -0,0 +1,14 @@
+'use strict'
+const u = require('universalify').fromPromise
+const { makeDir: _makeDir, makeDirSync } = require('./make-dir')
+const makeDir = u(_makeDir)
+
+module.exports = {
+  mkdirs: makeDir,
+  mkdirsSync: makeDirSync,
+  // alias
+  mkdirp: makeDir,
+  mkdirpSync: makeDirSync,
+  ensureDir: makeDir,
+  ensureDirSync: makeDirSync
+}