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/url-alphabet/index.cjs

@@ -0,0 +1,7 @@
+// This alphabet uses `A-Za-z0-9_-` symbols.
+// The order of characters is optimized for better gzip and brotli compression.
+// Same as in non-secure/index.js
+let urlAlphabet =
+  'useandom-26T198340PX75pxJACKVERYMINDBUSHWOLF_GQZbfghjklqvwyzrict'
+
+module.exports = { urlAlphabet }

pwa/node_modules/nanoid/url-alphabet/index.js

@@ -0,0 +1,3 @@
+let urlAlphabet =
+  'useandom-26T198340PX75pxJACKVERYMINDBUSHWOLF_GQZbfghjklqvwyzrict'
+export { urlAlphabet }

pwa/node_modules/nanoid/url-alphabet/package.json

@@ -0,0 +1,6 @@
+{
+  "type": "module",
+  "main": "index.cjs",
+  "module": "index.js",
+  "react-native": "index.js"
+}