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/leaflet.offline/rollup.config.mjs

@@ -0,0 +1,20 @@
+import resolve from '@rollup/plugin-node-resolve';
+import pkg from './package.json' with { type: 'json' };
+import typescript from '@rollup/plugin-typescript';
+
+const extensions = ['.ts'];
+
+export default {
+  input: 'src/index.ts',
+  output: {
+    file: pkg.main,
+    format: 'umd',
+    name: 'LeafletOffline',
+    globals: {
+      leaflet: 'L',
+      idb: 'idb',
+    },
+  },
+  plugins: [resolve({ extensions }), typescript()],
+  external: ['leaflet', 'idb'],
+};