Add keyboard search and the empty, loading, and error states.

CONTENT-WP-0002-T05 focuses search with slash, clears it with Escape, and wraps the header on a narrow screen.

Assistant: grok
Assistant-Session: 01a1346c-fdff-7741-b1af-b7283661554b

ui/app/loading.tsx

@@ -0,0 +1,7 @@
+export default function Loading() {
+  return (
+    <p className="mx-auto max-w-7xl px-4 py-14 text-sm text-muted sm:px-6" role="status" aria-busy="true">
+      Loading records.
+    </p>
+  );
+}