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/core-js-compat/shared.d.ts

@@ -0,0 +1,32 @@
+export type ModuleName = string;
+
+export type Target =
+  | 'android'
+  | 'bun'
+  | 'chrome'
+  | 'chrome-android'
+  | 'deno'
+  | 'edge'
+  | 'electron'
+  | 'firefox'
+  | 'firefox-android'
+  | 'hermes'
+  | 'ie'
+  | 'ios'
+  | 'node'
+  | 'opera'
+  | 'opera-android'
+  | 'phantom'
+  | 'quest'
+  | 'react-native'
+  | 'rhino'
+  | 'safari'
+  | 'samsung'
+  /** `quest` alias */
+  | 'oculus'
+  /** `react-native` alias */
+  | 'react'
+  /** @deprecated use `opera-android` instead */
+  | 'opera_mobile';
+
+export type TargetVersion = string;