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/jsonfile/index.js

@@ -0,0 +1,88 @@
+let _fs
+try {
+  _fs = require('graceful-fs')
+} catch (_) {
+  _fs = require('fs')
+}
+const universalify = require('universalify')
+const { stringify, stripBom } = require('./utils')
+
+async function _readFile (file, options = {}) {
+  if (typeof options === 'string') {
+    options = { encoding: options }
+  }
+
+  const fs = options.fs || _fs
+
+  const shouldThrow = 'throws' in options ? options.throws : true
+
+  let data = await universalify.fromCallback(fs.readFile)(file, options)
+
+  data = stripBom(data)
+
+  let obj
+  try {
+    obj = JSON.parse(data, options ? options.reviver : null)
+  } catch (err) {
+    if (shouldThrow) {
+      err.message = `${file}: ${err.message}`
+      throw err
+    } else {
+      return null
+    }
+  }
+
+  return obj
+}
+
+const readFile = universalify.fromPromise(_readFile)
+
+function readFileSync (file, options = {}) {
+  if (typeof options === 'string') {
+    options = { encoding: options }
+  }
+
+  const fs = options.fs || _fs
+
+  const shouldThrow = 'throws' in options ? options.throws : true
+
+  try {
+    let content = fs.readFileSync(file, options)
+    content = stripBom(content)
+    return JSON.parse(content, options.reviver)
+  } catch (err) {
+    if (shouldThrow) {
+      err.message = `${file}: ${err.message}`
+      throw err
+    } else {
+      return null
+    }
+  }
+}
+
+async function _writeFile (file, obj, options = {}) {
+  const fs = options.fs || _fs
+
+  const str = stringify(obj, options)
+
+  await universalify.fromCallback(fs.writeFile)(file, str, options)
+}
+
+const writeFile = universalify.fromPromise(_writeFile)
+
+function writeFileSync (file, obj, options = {}) {
+  const fs = options.fs || _fs
+
+  const str = stringify(obj, options)
+  // not sure if fs.writeFileSync returns anything, but just in case
+  return fs.writeFileSync(file, str, options)
+}
+
+// NOTE: do not change this export format; required for ESM compat
+// see https://github.com/jprichardson/node-jsonfile/pull/162 for details
+module.exports = {
+  readFile,
+  readFileSync,
+  writeFile,
+  writeFileSync
+}