Allow admin to preview unpublished lessons without enrollment

- Course layout skips enrollment and published checks for admin role
- Lesson page skips published filter for admin role
- Enables admin preview button to work for any lesson/course state

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

src/app/(student)/courses/[slug]/lessons/[lessonId]/page.tsx

@@ -1,6 +1,8 @@
 import { prisma } from "@/lib/prisma";
 import { notFound } from "next/navigation";
 import Link from "next/link";
+import { headers } from "next/headers";
+import { auth } from "@/lib/auth";
 import { KinescopePlayer } from "@/components/player/kinescope-player";
 import { LessonContent } from "@/components/student/lesson-content";
 
@@ -11,8 +13,11 @@ interface Props {
 export default async function LessonPage({ params }: Props) {
   const { slug, lessonId } = await params;
 
+  const session = await auth.api.getSession({ headers: await headers() });
+  const isAdmin = session?.user.role === "admin";
+
   const lesson = await prisma.lesson.findUnique({
-    where: { id: lessonId, published: true },
+    where: { id: lessonId, ...(isAdmin ? {} : { published: true }) },
     include: {
       files: { orderBy: { createdAt: "asc" } },
       module: {