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/buffer-from/index.js

@@ -0,0 +1,72 @@
+/* eslint-disable node/no-deprecated-api */
+
+var toString = Object.prototype.toString
+
+var isModern = (
+  typeof Buffer !== 'undefined' &&
+  typeof Buffer.alloc === 'function' &&
+  typeof Buffer.allocUnsafe === 'function' &&
+  typeof Buffer.from === 'function'
+)
+
+function isArrayBuffer (input) {
+  return toString.call(input).slice(8, -1) === 'ArrayBuffer'
+}
+
+function fromArrayBuffer (obj, byteOffset, length) {
+  byteOffset >>>= 0
+
+  var maxLength = obj.byteLength - byteOffset
+
+  if (maxLength < 0) {
+    throw new RangeError("'offset' is out of bounds")
+  }
+
+  if (length === undefined) {
+    length = maxLength
+  } else {
+    length >>>= 0
+
+    if (length > maxLength) {
+      throw new RangeError("'length' is out of bounds")
+    }
+  }
+
+  return isModern
+    ? Buffer.from(obj.slice(byteOffset, byteOffset + length))
+    : new Buffer(new Uint8Array(obj.slice(byteOffset, byteOffset + length)))
+}
+
+function fromString (string, encoding) {
+  if (typeof encoding !== 'string' || encoding === '') {
+    encoding = 'utf8'
+  }
+
+  if (!Buffer.isEncoding(encoding)) {
+    throw new TypeError('"encoding" must be a valid string encoding')
+  }
+
+  return isModern
+    ? Buffer.from(string, encoding)
+    : new Buffer(string, encoding)
+}
+
+function bufferFrom (value, encodingOrOffset, length) {
+  if (typeof value === 'number') {
+    throw new TypeError('"value" argument must not be a number')
+  }
+
+  if (isArrayBuffer(value)) {
+    return fromArrayBuffer(value, encodingOrOffset, length)
+  }
+
+  if (typeof value === 'string') {
+    return fromString(value, encodingOrOffset)
+  }
+
+  return isModern
+    ? Buffer.from(value)
+    : new Buffer(value)
+}
+
+module.exports = bufferFrom