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.browser.js

@@ -0,0 +1,34 @@
+let random = async bytes => crypto.getRandomValues(new Uint8Array(bytes))
+let customAlphabet = (alphabet, defaultSize = 21) => {
+  let mask = (2 << (Math.log(alphabet.length - 1) / Math.LN2)) - 1
+  let step = -~((1.6 * mask * defaultSize) / alphabet.length)
+  return async (size = defaultSize) => {
+    let id = ''
+    while (true) {
+      let bytes = crypto.getRandomValues(new Uint8Array(step))
+      let i = step | 0
+      while (i--) {
+        id += alphabet[bytes[i] & mask] || ''
+        if (id.length === size) return id
+      }
+    }
+  }
+}
+let nanoid = async (size = 21) => {
+  let id = ''
+  let bytes = crypto.getRandomValues(new Uint8Array((size |= 0)))
+  while (size--) {
+    let byte = bytes[size] & 63
+    if (byte < 36) {
+      id += byte.toString(36)
+    } else if (byte < 62) {
+      id += (byte - 26).toString(36).toUpperCase()
+    } else if (byte < 63) {
+      id += '_'
+    } else {
+      id += '-'
+    }
+  }
+  return id
+}
+export { nanoid, customAlphabet, random }