Feature 06: PWA shell and offline (#58)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>

web/src/pwa/OfflinePill.tsx

@@ -0,0 +1,19 @@
+import { useSyncExternalStore } from 'react'
+import { WifiOff } from 'lucide-react'
+import { useApi } from '../api/index.ts'
+import { Icon } from '../ui/Icon.tsx'
+import styles from './OfflinePill.module.css'
+
+// OfflinePill tells the household that what they see came from the cache
+// while the browser is offline or the server cannot be reached.
+export function OfflinePill() {
+  const { network } = useApi()
+  const offline = useSyncExternalStore(network.subscribe, network.offline)
+  if (!offline) return null
+  return (
+    <p role="status" className={styles.pill}>
+      <Icon icon={WifiOff} />
+      Offline — showing saved data
+    </p>
+  )
+}