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/ajv/lib/runtime/ucs2length.ts

@@ -0,0 +1,20 @@
+// https://mathiasbynens.be/notes/javascript-encoding
+// https://github.com/bestiejs/punycode.js - punycode.ucs2.decode
+export default function ucs2length(str: string): number {
+  const len = str.length
+  let length = 0
+  let pos = 0
+  let value: number
+  while (pos < len) {
+    length++
+    value = str.charCodeAt(pos++)
+    if (value >= 0xd800 && value <= 0xdbff && pos < len) {
+      // high surrogate, and there is a next character
+      value = str.charCodeAt(pos)
+      if ((value & 0xfc00) === 0xdc00) pos++ // low surrogate
+    }
+  }
+  return length
+}
+
+ucs2length.code = 'require("ajv/dist/runtime/ucs2length").default'