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/foreground-child/dist/esm/all-signals.js

@@ -0,0 +1,52 @@
+import constants from 'node:constants';
+export const allSignals = 
+// this is the full list of signals that Node will let us do anything with
+Object.keys(constants).filter(k => k.startsWith('SIG') &&
+    // https://github.com/tapjs/signal-exit/issues/21
+    k !== 'SIGPROF' &&
+    // no sense trying to listen for SIGKILL, it's impossible
+    k !== 'SIGKILL');
+// These are some obscure signals that are reported by kill -l
+// on macOS, Linux, or Windows, but which don't have any mapping
+// in Node.js. No sense trying if they're just going to throw
+// every time on every platform.
+//
+// 'SIGEMT',
+// 'SIGLOST',
+// 'SIGPOLL',
+// 'SIGRTMAX',
+// 'SIGRTMAX-1',
+// 'SIGRTMAX-10',
+// 'SIGRTMAX-11',
+// 'SIGRTMAX-12',
+// 'SIGRTMAX-13',
+// 'SIGRTMAX-14',
+// 'SIGRTMAX-15',
+// 'SIGRTMAX-2',
+// 'SIGRTMAX-3',
+// 'SIGRTMAX-4',
+// 'SIGRTMAX-5',
+// 'SIGRTMAX-6',
+// 'SIGRTMAX-7',
+// 'SIGRTMAX-8',
+// 'SIGRTMAX-9',
+// 'SIGRTMIN',
+// 'SIGRTMIN+1',
+// 'SIGRTMIN+10',
+// 'SIGRTMIN+11',
+// 'SIGRTMIN+12',
+// 'SIGRTMIN+13',
+// 'SIGRTMIN+14',
+// 'SIGRTMIN+15',
+// 'SIGRTMIN+16',
+// 'SIGRTMIN+2',
+// 'SIGRTMIN+3',
+// 'SIGRTMIN+4',
+// 'SIGRTMIN+5',
+// 'SIGRTMIN+6',
+// 'SIGRTMIN+7',
+// 'SIGRTMIN+8',
+// 'SIGRTMIN+9',
+// 'SIGSTKFLT',
+// 'SIGUNUSED',
+//# sourceMappingURL=all-signals.js.map