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/workbox-build/.ncurc.js

@@ -0,0 +1,19 @@
+/*
+  Copyright 2020 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+
+// We use `npx npm-check-updates` to find updates to dependencies.
+// Some dependencies have breaking changes that we can't resolve.
+// This config file excludes those dependencies from the checks
+// until we're able to remediate our code to deal with them.
+module.exports = {
+  reject: [
+    // joi v16 is the last release to support Node v10:
+    // https://github.com/sideway/joi/issues/2262
+    '@hapi/joi',
+  ],
+};