Fix impersonation: hard navigation + stop impersonating banner

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/(student)/layout.tsx

@@ -4,6 +4,7 @@ import { redirect } from "next/navigation";
 import Link from "next/link";
 import { LogoutButton } from "@/components/layout/logout-button";
 import { getSetting } from "@/lib/settings";
+import { StopImpersonateBanner } from "@/components/admin/stop-impersonate-banner";
 
 export default async function StudentLayout({ children }: { children: React.ReactNode }) {
   const session = await auth.api.getSession({ headers: await headers() });
@@ -15,8 +16,11 @@ export default async function StudentLayout({ children }: { children: React.Reac
     if (maintenance === "true") redirect("/maintenance");
   }
 
+  const isImpersonating = !!(session.session as { impersonatedBy?: string }).impersonatedBy;
+
   return (
     <div className="min-h-screen flex flex-col" style={{ backgroundColor: "var(--background)" }}>
+      {isImpersonating && <StopImpersonateBanner userName={session.user.name} />}
       <header
         className="sticky top-0 z-10 flex items-center justify-between px-6 py-3"
         style={{ borderBottom: "2px solid var(--border)", backgroundColor: "var(--background)" }}