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/lodash.debounce/README.md

@@ -0,0 +1,18 @@
+# lodash.debounce v4.0.8
+
+The [lodash](https://lodash.com/) method `_.debounce` exported as a [Node.js](https://nodejs.org/) module.
+
+## Installation
+
+Using npm:
+```bash
+$ {sudo -H} npm i -g npm
+$ npm i --save lodash.debounce
+```
+
+In Node.js:
+```js
+var debounce = require('lodash.debounce');
+```
+
+See the [documentation](https://lodash.com/docs#debounce) or [package source](https://github.com/lodash/lodash/blob/4.0.8-npm-packages/lodash.debounce) for more details.