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/gensync/index.js.flow

@@ -0,0 +1,32 @@
+// @flow
+
+opaque type Next = Function | void;
+opaque type Yield = mixed;
+
+export type Gensync<Args, Return> = {
+  (...args: Args): Handler<Return>,
+  sync(...args: Args): Return,
+  async(...args: Args): Promise<Return>,
+  // ...args: [...Args, Callback]
+  errback(...args: any[]): void,
+};
+
+export type Handler<Return> = Generator<Yield, Return, Next>;
+export type Options<Args, Return> = {
+  sync(...args: Args): Return,
+  arity?: number,
+  name?: string,
+} & (
+  | { async?: (...args: Args) => Promise<Return> }
+  // ...args: [...Args, Callback]
+  | { errback(...args: any[]): void }
+);
+
+declare module.exports: {
+  <Args, Return>(
+    Options<Args, Return> | ((...args: Args) => Handler<Return>)
+  ): Gensync<Args, Return>,
+
+  all<Return>(Array<Handler<Return>>): Handler<Return[]>,
+  race<Return>(Array<Handler<Return>>): Handler<Return>,
+};