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/output/index.js

@@ -0,0 +1,40 @@
+'use strict'
+
+const u = require('universalify').fromCallback
+const fs = require('graceful-fs')
+const path = require('path')
+const mkdir = require('../mkdirs')
+const pathExists = require('../path-exists').pathExists
+
+function outputFile (file, data, encoding, callback) {
+  if (typeof encoding === 'function') {
+    callback = encoding
+    encoding = 'utf8'
+  }
+
+  const dir = path.dirname(file)
+  pathExists(dir, (err, itDoes) => {
+    if (err) return callback(err)
+    if (itDoes) return fs.writeFile(file, data, encoding, callback)
+
+    mkdir.mkdirs(dir, err => {
+      if (err) return callback(err)
+
+      fs.writeFile(file, data, encoding, callback)
+    })
+  })
+}
+
+function outputFileSync (file, ...args) {
+  const dir = path.dirname(file)
+  if (fs.existsSync(dir)) {
+    return fs.writeFileSync(file, ...args)
+  }
+  mkdir.mkdirsSync(dir)
+  fs.writeFileSync(file, ...args)
+}
+
+module.exports = {
+  outputFile: u(outputFile),
+  outputFileSync
+}