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/vitest/suppress-warnings.cjs

@@ -0,0 +1,21 @@
+// borrowed from tsx implementation:
+// https://github.com/esbuild-kit/tsx
+
+const ignoreWarnings = new Set([
+  '--experimental-loader is an experimental feature. This feature could change at any time',
+  'Custom ESM Loaders is an experimental feature. This feature could change at any time',
+  'Custom ESM Loaders is an experimental feature and might change at any time',
+  'VM Modules is an experimental feature and might change at any time',
+  'VM Modules is an experimental feature. This feature could change at any time',
+])
+
+const { emit } = process
+
+process.emit = function (event, warning) {
+  if (event === 'warning' && ignoreWarnings.has(warning.message)) {
+    return
+  }
+
+  // eslint-disable-next-line prefer-rest-params
+  return Reflect.apply(emit, this, arguments)
+}