feat(inquiries): top-level Inquiries page (list + detail + convert), nav entries; retire admin inbox

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/(dashboard)/[portSlug]/inquiries/[id]/loading.tsx

@@ -0,0 +1,11 @@
+import { Skeleton } from '@/components/ui/skeleton';
+
+export default function Loading() {
+  return (
+    <div className="space-y-4">
+      <Skeleton className="h-16 w-full" />
+      <Skeleton className="h-8 w-64" />
+      <Skeleton className="h-64 w-full" />
+    </div>
+  );
+}