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/@vitest/expect/README.md

@@ -0,0 +1,21 @@
+# @vitest/expect
+
+Jest's expect matchers as a Chai plugin.
+
+## Usage
+
+```js
+import {
+  JestAsymmetricMatchers,
+  JestChaiExpect,
+  JestExtend,
+} from '@vitest/expect'
+import * as chai from 'chai'
+
+// allows using expect.extend instead of chai.use to extend plugins
+chai.use(JestExtend)
+// adds all jest matchers to expect
+chai.use(JestChaiExpect)
+// adds asymmetric matchers like stringContaining, objectContaining
+chai.use(JestAsymmetricMatchers)
+```