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/non-secure/index.cjs

@@ -0,0 +1,34 @@
+// This alphabet uses `A-Za-z0-9_-` symbols.
+// The order of characters is optimized for better gzip and brotli compression.
+// References to the same file (works both for gzip and brotli):
+// `'use`, `andom`, and `rict'`
+// References to the brotli default dictionary:
+// `-26T`, `1983`, `40px`, `75px`, `bush`, `jack`, `mind`, `very`, and `wolf`
+let urlAlphabet =
+  'useandom-26T198340PX75pxJACKVERYMINDBUSHWOLF_GQZbfghjklqvwyzrict'
+
+let customAlphabet = (alphabet, defaultSize = 21) => {
+  return (size = defaultSize) => {
+    let id = ''
+    // A compact alternative for `for (var i = 0; i < step; i++)`.
+    let i = size | 0
+    while (i--) {
+      // `| 0` is more compact and faster than `Math.floor()`.
+      id += alphabet[(Math.random() * alphabet.length) | 0]
+    }
+    return id
+  }
+}
+
+let nanoid = (size = 21) => {
+  let id = ''
+  // A compact alternative for `for (var i = 0; i < step; i++)`.
+  let i = size | 0
+  while (i--) {
+    // `| 0` is more compact and faster than `Math.floor()`.
+    id += urlAlphabet[(Math.random() * 64) | 0]
+  }
+  return id
+}
+
+module.exports = { nanoid, customAlphabet }