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/link.js

@@ -0,0 +1,61 @@
+'use strict'
+
+const u = require('universalify').fromCallback
+const path = require('path')
+const fs = require('graceful-fs')
+const mkdir = require('../mkdirs')
+const pathExists = require('../path-exists').pathExists
+
+function createLink (srcpath, dstpath, callback) {
+  function makeLink (srcpath, dstpath) {
+    fs.link(srcpath, dstpath, err => {
+      if (err) return callback(err)
+      callback(null)
+    })
+  }
+
+  pathExists(dstpath, (err, destinationExists) => {
+    if (err) return callback(err)
+    if (destinationExists) return callback(null)
+    fs.lstat(srcpath, (err) => {
+      if (err) {
+        err.message = err.message.replace('lstat', 'ensureLink')
+        return callback(err)
+      }
+
+      const dir = path.dirname(dstpath)
+      pathExists(dir, (err, dirExists) => {
+        if (err) return callback(err)
+        if (dirExists) return makeLink(srcpath, dstpath)
+        mkdir.mkdirs(dir, err => {
+          if (err) return callback(err)
+          makeLink(srcpath, dstpath)
+        })
+      })
+    })
+  })
+}
+
+function createLinkSync (srcpath, dstpath) {
+  const destinationExists = fs.existsSync(dstpath)
+  if (destinationExists) return undefined
+
+  try {
+    fs.lstatSync(srcpath)
+  } catch (err) {
+    err.message = err.message.replace('lstat', 'ensureLink')
+    throw err
+  }
+
+  const dir = path.dirname(dstpath)
+  const dirExists = fs.existsSync(dir)
+  if (dirExists) return fs.linkSync(srcpath, dstpath)
+  mkdir.mkdirsSync(dir)
+
+  return fs.linkSync(srcpath, dstpath)
+}
+
+module.exports = {
+  createLink: u(createLink),
+  createLinkSync
+}