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/regexpu-core/rewrite-pattern.d.ts

@@ -0,0 +1,17 @@
+declare module "regexpu-core" {
+  export type RegexpuOptions = {
+    unicodeFlag?: "transform" | false;
+    unicodeSetsFlag?: "transform" | false;
+    dotAllFlag?: "transform" | false;
+    unicodePropertyEscapes?: "transform" | false;
+    namedGroups?: "transform" | false;
+    onNamedGroup?: (name: string, index: number) => void;
+    modifiers?: "transform" | false | "parse";
+    onNewFlags?: (flags: string) => void;
+  };
+  export default function rewritePattern(
+    pattern: string,
+    flags: string,
+    options: RegexpuOptions | undefined
+  ): string;
+}