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/unbox-primitive/index.d.ts

@@ -0,0 +1,13 @@
+declare function unboxPrimitive<T extends unboxPrimitive.Boxed>(value: T): unboxPrimitive.Unbox<T>;
+
+declare namespace unboxPrimitive {
+    type Boxed = String | Number | Boolean | Symbol | BigInt;
+    type Unbox<T extends Boxed> = T extends String ? string
+        : T extends Number ? number
+        : T extends Boolean ? boolean
+        : T extends Symbol ? symbol
+        : T extends BigInt ? bigint
+        : never;
+}
+
+export = unboxPrimitive;