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/fast-json-stable-stringify/example/key_cmp.js

@@ -0,0 +1,7 @@
+var stringify = require('../');
+
+var obj = { c: 8, b: [{z:6,y:5,x:4},7], a: 3 };
+var s = stringify(obj, function (a, b) {
+    return a.key < b.key ? 1 : -1;
+});
+console.log(s);