Add course management improvements: tree view, module descriptions, lesson toggles

- SortableModules: add description textarea in edit form, show description in row
- CourseDetailPage: fetch lessons per module, add CourseTree overview section
- ModulePage: fetch sibling modules, pass as otherModules to SortableLessons

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

src/app/admin/courses/[courseId]/modules/[moduleId]/page.tsx

@@ -10,13 +10,20 @@ interface Props {
 export default async function ModulePage({ params }: Props) {
   const { courseId, moduleId } = await params;
 
-  const module = await prisma.module.findUnique({
-    where: { id: moduleId },
-    include: {
-      course: { select: { title: true } },
-      lessons: { orderBy: { order: "asc" } },
-    },
-  });
+  const [module, allModules] = await Promise.all([
+    prisma.module.findUnique({
+      where: { id: moduleId },
+      include: {
+        course: { select: { title: true } },
+        lessons: { orderBy: { order: "asc" } },
+      },
+    }),
+    prisma.module.findMany({
+      where: { courseId, NOT: { id: moduleId } },
+      select: { id: true, title: true },
+      orderBy: { order: "asc" },
+    }),
+  ]);
 
   if (!module || module.courseId !== courseId) notFound();
 
@@ -41,7 +48,12 @@ export default async function ModulePage({ params }: Props) {
         <p className="text-xs font-bold uppercase tracking-widest mb-5" style={{ color: "var(--muted-foreground)" }}>
           Уроки модуля
         </p>
-        <SortableLessons courseId={courseId} moduleId={moduleId} lessons={module.lessons} />
+        <SortableLessons
+          courseId={courseId}
+          moduleId={moduleId}
+          lessons={module.lessons}
+          otherModules={allModules}
+        />
       </section>
     </div>
   );