fix(app): add the App Router root layout so the control-plane app can build (coreci-chat#10)

apps/control-plane/app/layout.tsx

@@ -0,0 +1,27 @@
+/**
+ * / - App Router root layout (coreci-chat#10).
+ *
+ * Next.js 15 requires a root layout that renders <html> and <body> above
+ * every route. Without one, `next build` fails with "login/page.tsx does not
+ * have a root layout", so apps/control-plane has never been buildable - the
+ * pipeline never built the app, so nothing caught it.
+ *
+ * This is the build-enabling minimum only. The shell content (theme,
+ * providers, session wrapper) is an M3 scope call for the line head and is
+ * deliberately NOT decided here - it rides the M3 kickoff verdict on
+ * coreci-chat#1.
+ */
+
+import type { ReactNode } from "react";
+
+export const metadata = {
+  title: "CoreCI Chat - control plane",
+};
+
+export default function RootLayout({ children }: { children: ReactNode }) {
+  return (
+    <html lang="en">
+      <body>{children}</body>
+    </html>
+  );
+}