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/unique-string/readme.md

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+# unique-string [![Build Status](https://travis-ci.org/sindresorhus/unique-string.svg?branch=master)](https://travis-ci.org/sindresorhus/unique-string)
+
+> Generate a unique random string
+
+
+## Install
+
+```
+$ npm install unique-string
+```
+
+
+## Usage
+
+```js
+const uniqueString = require('unique-string');
+
+uniqueString();
+//=> 'b4de2a49c8ffa3fbee04446f045483b2'
+```
+
+
+## API
+
+### uniqueString()
+
+Returns a 32 character unique string. Matches the length of MD5, which is [unique enough](https://stackoverflow.com/a/2444336/64949) for non-crypto purposes.
+
+
+## License
+
+MIT © [Sindre Sorhus](https://sindresorhus.com)