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/async/bower.json

@@ -0,0 +1,17 @@
+{
+  "name": "async",
+  "main": "dist/async.js",
+  "ignore": [
+    "bower_components",
+    "lib",
+    "test",
+    "node_modules",
+    "perf",
+    "support",
+    "**/.*",
+    "*.config.js",
+    "*.json",
+    "index.js",
+    "Makefile"
+  ]
+}