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/package.json

@@ -0,0 +1,31 @@
+{
+  "name": "core-js-compat",
+  "version": "3.48.0",
+  "type": "commonjs",
+  "description": "core-js compat",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/zloirock/core-js.git",
+    "directory": "packages/core-js-compat"
+  },
+  "homepage": "https://core-js.io",
+  "bugs": {
+    "url": "https://github.com/zloirock/core-js/issues"
+  },
+  "funding": {
+    "type": "opencollective",
+    "url": "https://opencollective.com/core-js"
+  },
+  "license": "MIT",
+  "author": {
+    "name": "Denis Pushkarev",
+    "email": "zloirock@zloirock.ru",
+    "url": "http://zloirock.ru"
+  },
+  "sideEffects": false,
+  "main": "index.js",
+  "types": "index.d.ts",
+  "dependencies": {
+    "browserslist": "^4.28.1"
+  }
+}