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/watchdog.js

@@ -0,0 +1,46 @@
+// this spawns a child process that listens for SIGHUP when the
+// parent process exits, and after 200ms, sends a SIGKILL to the
+// child, in case it did not terminate.
+import { spawn } from 'child_process';
+const watchdogCode = String.raw `
+const pid = parseInt(process.argv[1], 10)
+process.title = 'node (foreground-child watchdog pid=' + pid + ')'
+if (!isNaN(pid)) {
+  let barked = false
+  // keepalive
+  const interval = setInterval(() => {}, 60000)
+  const bark = () => {
+    clearInterval(interval)
+    if (barked) return
+    barked = true
+    process.removeListener('SIGHUP', bark)
+    setTimeout(() => {
+      try {
+        process.kill(pid, 'SIGKILL')
+        setTimeout(() => process.exit(), 200)
+      } catch (_) {}
+    }, 500)
+  })
+  process.on('SIGHUP', bark)
+}
+`;
+/**
+ * Pass in a ChildProcess, and this will spawn a watchdog process that
+ * will make sure it exits if the parent does, thus preventing any
+ * dangling detached zombie processes.
+ *
+ * If the child ends before the parent, then the watchdog will terminate.
+ */
+export const watchdog = (child) => {
+    let dogExited = false;
+    const dog = spawn(process.execPath, ['-e', watchdogCode, String(child.pid)], {
+        stdio: 'ignore',
+    });
+    dog.on('exit', () => (dogExited = true));
+    child.on('exit', () => {
+        if (!dogExited)
+            dog.kill('SIGKILL');
+    });
+    return dog;
+};
+//# sourceMappingURL=watchdog.js.map