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/universalify/index.js

@@ -0,0 +1,24 @@
+'use strict'
+
+exports.fromCallback = function (fn) {
+  return Object.defineProperty(function (...args) {
+    if (typeof args[args.length - 1] === 'function') fn.apply(this, args)
+    else {
+      return new Promise((resolve, reject) => {
+        args.push((err, res) => (err != null) ? reject(err) : resolve(res))
+        fn.apply(this, args)
+      })
+    }
+  }, 'name', { value: fn.name })
+}
+
+exports.fromPromise = function (fn) {
+  return Object.defineProperty(function (...args) {
+    const cb = args[args.length - 1]
+    if (typeof cb !== 'function') return fn.apply(this, args)
+    else {
+      args.pop()
+      fn.apply(this, args).then(r => cb(null, r), cb)
+    }
+  }, 'name', { value: fn.name })
+}