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/assertion-error/index.d.ts

@@ -0,0 +1,27 @@
+interface Result {
+  name: "AssertionError" | "AssertionResult";
+  ok: boolean;
+  toJSON(...args: unknown[]): Record<string, unknown>;
+}
+
+declare class AssertionError<T> extends Error implements Result {
+  [key: string]: unknown
+  name: "AssertionError";
+  ok: false;
+  message: string;
+  // deno-lint-ignore ban-types
+  constructor(message: string, props?: T, ssf?: Function);
+  stack: string;
+  toJSON(stack?: boolean): Record<string, unknown>;
+}
+
+declare class AssertionResult<T> implements Result {
+  [key: string]: unknown
+  name: "AssertionResult";
+  ok: true;
+  message: string;
+  constructor(props?: T);
+  toJSON(): Record<string, unknown>;
+}
+
+export { AssertionError, AssertionResult, Result };