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/file.js

@@ -0,0 +1,69 @@
+'use strict'
+
+const u = require('universalify').fromCallback
+const path = require('path')
+const fs = require('graceful-fs')
+const mkdir = require('../mkdirs')
+
+function createFile (file, callback) {
+  function makeFile () {
+    fs.writeFile(file, '', err => {
+      if (err) return callback(err)
+      callback()
+    })
+  }
+
+  fs.stat(file, (err, stats) => { // eslint-disable-line handle-callback-err
+    if (!err && stats.isFile()) return callback()
+    const dir = path.dirname(file)
+    fs.stat(dir, (err, stats) => {
+      if (err) {
+        // if the directory doesn't exist, make it
+        if (err.code === 'ENOENT') {
+          return mkdir.mkdirs(dir, err => {
+            if (err) return callback(err)
+            makeFile()
+          })
+        }
+        return callback(err)
+      }
+
+      if (stats.isDirectory()) makeFile()
+      else {
+        // parent is not a directory
+        // This is just to cause an internal ENOTDIR error to be thrown
+        fs.readdir(dir, err => {
+          if (err) return callback(err)
+        })
+      }
+    })
+  })
+}
+
+function createFileSync (file) {
+  let stats
+  try {
+    stats = fs.statSync(file)
+  } catch {}
+  if (stats && stats.isFile()) return
+
+  const dir = path.dirname(file)
+  try {
+    if (!fs.statSync(dir).isDirectory()) {
+      // parent is not a directory
+      // This is just to cause an internal ENOTDIR error to be thrown
+      fs.readdirSync(dir)
+    }
+  } catch (err) {
+    // If the stat call above failed because the directory doesn't exist, create it
+    if (err && err.code === 'ENOENT') mkdir.mkdirsSync(dir)
+    else throw err
+  }
+
+  fs.writeFileSync(file, '')
+}
+
+module.exports = {
+  createFile: u(createFile),
+  createFileSync
+}