Fix impersonation: use direct fetch to /api/auth/admin/impersonate-user

authClient.admin.impersonateUser is not registered in pathMethods
in better-auth v1.6 client plugin — call the endpoint directly.

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

src/components/admin/users-table.tsx

@@ -1,10 +1,8 @@
 "use client";
 
 import { useState } from "react";
-import { useRouter } from "next/navigation";
 import Link from "next/link";
 import { Badge } from "@/components/ui/badge";
-import { authClient } from "@/lib/auth-client";
 
 type Enrollment = {
   courseId: string;
@@ -93,15 +91,21 @@ function UserPopup({ user }: { user: UserRow }) {
 }
 
 function ImpersonateButton({ userId }: { userId: string }) {
-  const router = useRouter();
   const [loading, setLoading] = useState(false);
 
   async function handleImpersonate() {
     setLoading(true);
     try {
-      await authClient.admin.impersonateUser({ userId });
+      const res = await fetch("/api/auth/admin/impersonate-user", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ userId }),
+        credentials: "include",
+      });
+      if (!res.ok) throw new Error(await res.text());
       window.location.href = "/dashboard";
-    } catch {
+    } catch (e) {
+      console.error("Impersonation failed:", e);
       setLoading(false);
     }
   }