fix: /demos/[vertical] route with Next.js 15 params await

- Fix Next.js 15 params requirement (await params)
- Add minimal test for route redirect behavior
- Test verifies all 4 verticals redirect correctly

app/demos/[vertical]/page.tsx

@@ -0,0 +1,8 @@
+import { redirect } from 'next/navigation';
+
+// Next.js 15 requires params to be awaited
+export default async function DemoVerticalPage({ params }: { params: Promise<{ vertical: string }> }) {
+  const { vertical } = await params;
+  // Redirect to the main demos page with the vertical as query param
+  redirect(`/demos?vertical=${vertical}`);
+}