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/index.js

@@ -0,0 +1,45 @@
+import crypto from 'crypto'
+import { urlAlphabet } from './url-alphabet/index.js'
+const POOL_SIZE_MULTIPLIER = 128
+let pool, poolOffset
+let fillPool = bytes => {
+  if (!pool || pool.length < bytes) {
+    pool = Buffer.allocUnsafe(bytes * POOL_SIZE_MULTIPLIER)
+    crypto.randomFillSync(pool)
+    poolOffset = 0
+  } else if (poolOffset + bytes > pool.length) {
+    crypto.randomFillSync(pool)
+    poolOffset = 0
+  }
+  poolOffset += bytes
+}
+let random = bytes => {
+  fillPool((bytes |= 0))
+  return pool.subarray(poolOffset - bytes, poolOffset)
+}
+let customRandom = (alphabet, defaultSize, getRandom) => {
+  let mask = (2 << (31 - Math.clz32((alphabet.length - 1) | 1))) - 1
+  let step = Math.ceil((1.6 * mask * defaultSize) / alphabet.length)
+  return (size = defaultSize) => {
+    let id = ''
+    while (true) {
+      let bytes = getRandom(step)
+      let i = step
+      while (i--) {
+        id += alphabet[bytes[i] & mask] || ''
+        if (id.length === size) return id
+      }
+    }
+  }
+}
+let customAlphabet = (alphabet, size = 21) =>
+  customRandom(alphabet, size, random)
+let nanoid = (size = 21) => {
+  fillPool((size |= 0))
+  let id = ''
+  for (let i = poolOffset - size; i < poolOffset; i++) {
+    id += urlAlphabet[pool[i] & 63]
+  }
+  return id
+}
+export { nanoid, customAlphabet, customRandom, urlAlphabet, random }