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/signal-exit/dist/mjs/browser.d.ts

@@ -0,0 +1,12 @@
+/**
+ * This is a browser shim that provides the same functional interface
+ * as the main node export, but it does nothing.
+ * @module
+ */
+import type { Handler } from './index.js';
+export declare const onExit: (cb: Handler, opts: {
+    alwaysLast?: boolean;
+}) => () => void;
+export declare const load: () => void;
+export declare const unload: () => void;
+//# sourceMappingURL=browser.d.ts.map