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/core-js-compat/README.md

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+`core-js-compat` exposes some files as JSON, and they cannot be
+imported by Node.js ESM files.
+This folder proxies `core-js-compat` to ensure that every entry
+is CJS and can be safely imported.

pwa/node_modules/babel-plugin-polyfill-corejs3/core-js-compat/data.js

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+module.exports = require("core-js-compat/data");

pwa/node_modules/babel-plugin-polyfill-corejs3/core-js-compat/entries.js

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+module.exports = require("core-js-compat/entries");

pwa/node_modules/babel-plugin-polyfill-corejs3/core-js-compat/get-modules-list-for-target-version.js

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+module.exports = require("core-js-compat/get-modules-list-for-target-version");