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/babel-plugin-polyfill-corejs3/lib/shipped-proposals.js

@@ -0,0 +1,6 @@
+"use strict";
+
+exports.__esModule = true;
+exports.default = void 0;
+// This file is automatically generated by scripts/build-corejs3-shipped-proposals.mjs
+var _default = exports.default = new Set(["esnext.array.group", "esnext.array.group-to-map", "esnext.iterator.zip", "esnext.iterator.zip-keyed", "esnext.symbol.metadata"]);