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/nanoid/async/index.native.js

@@ -0,0 +1,26 @@
+import { getRandomBytesAsync } from 'expo-random'
+import { urlAlphabet } from '../url-alphabet/index.js'
+let random = getRandomBytesAsync
+let customAlphabet = (alphabet, defaultSize = 21) => {
+  let mask = (2 << (31 - Math.clz32((alphabet.length - 1) | 1))) - 1
+  let step = Math.ceil((1.6 * mask * defaultSize) / alphabet.length)
+  let tick = (id, size = defaultSize) =>
+    random(step).then(bytes => {
+      let i = step
+      while (i--) {
+        id += alphabet[bytes[i] & mask] || ''
+        if (id.length >= size) return id
+      }
+      return tick(id, size)
+    })
+  return size => tick('', size)
+}
+let nanoid = (size = 21) =>
+  random((size |= 0)).then(bytes => {
+    let id = ''
+    while (size--) {
+      id += urlAlphabet[bytes[size] & 63]
+    }
+    return id
+  })
+export { nanoid, customAlphabet, random }