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/@jridgewell/trace-mapping/src/strip-filename.ts

@@ -0,0 +1,8 @@
+/**
+ * Removes everything after the last "/", but leaves the slash.
+ */
+export default function stripFilename(path: string | undefined | null): string {
+  if (!path) return '';
+  const index = path.lastIndexOf('/');
+  return path.slice(0, index + 1);
+}