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/browserslist/error.js

@@ -0,0 +1,12 @@
+function BrowserslistError(message) {
+  this.name = 'BrowserslistError'
+  this.message = message
+  this.browserslist = true
+  if (Error.captureStackTrace) {
+    Error.captureStackTrace(this, BrowserslistError)
+  }
+}
+
+BrowserslistError.prototype = Error.prototype
+
+module.exports = BrowserslistError