Add cross-module lesson navigation and admin edit button

- Admin lesson editor now navigates across module boundaries (full course flat list)
- Student lesson view shows "Edit" button for admins linking to lesson editor

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

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

@@ -107,6 +107,18 @@ export default async function LessonPage({ params }: Props) {
 
   return (
     <article className="max-w-3xl mx-auto px-6 py-8">
+      {/* Admin edit bar */}
+      {isAdmin && (
+        <div className="flex items-center justify-end mb-4">
+          <Link
+            href={`/admin/courses/${lesson.module.course.id}/modules/${lesson.moduleId}/lessons/${lessonId}`}
+            className="btn-aubade text-xs px-3 py-1.5"
+          >
+            Редактировать урок
+          </Link>
+        </div>
+      )}
+
       {/* Title */}
       <h1 className="text-2xl font-bold mb-6 leading-snug">{lesson.title}</h1>
 

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

@@ -13,7 +13,7 @@ interface Props {
 export default async function LessonEditorPage({ params }: Props) {
   const { courseId, moduleId, lessonId } = await params;
 
-  const [lesson, siblings] = await Promise.all([
+  const [lesson, allCourseLessons] = await Promise.all([
     prisma.lesson.findUnique({
       where: { id: lessonId },
       include: {
@@ -28,29 +28,27 @@ export default async function LessonEditorPage({ params }: Props) {
       },
     }),
     prisma.lesson.findMany({
-      where: { moduleId },
-      orderBy: { order: "asc" },
-      select: { id: true, title: true },
+      where: { module: { courseId } },
+      orderBy: [{ module: { order: "asc" } }, { order: "asc" }],
+      select: { id: true, title: true, moduleId: true },
     }),
   ]);
 
   if (!lesson || lesson.moduleId !== moduleId) notFound();
 
-  const idx = siblings.findIndex((l) => l.id === lessonId);
-  const prevLesson = idx > 0 ? siblings[idx - 1] : null;
-  const nextLesson = idx < siblings.length - 1 ? siblings[idx + 1] : null;
+  const idx = allCourseLessons.findIndex((l) => l.id === lessonId);
+  const prevLesson = idx > 0 ? allCourseLessons[idx - 1] : null;
+  const nextLesson = idx < allCourseLessons.length - 1 ? allCourseLessons[idx + 1] : null;
 
   // Serialize all Prisma proxy objects (DateTime, relations) before passing to Client Components
   const plain = JSON.parse(JSON.stringify({
     files: lesson.files,
     homework: lesson.homework,
     quiz: lesson.quiz,
-    siblings,
   })) as {
     files: typeof lesson.files;
     homework: typeof lesson.homework;
     quiz: typeof lesson.quiz;
-    siblings: typeof siblings;
   };
 
   return (
@@ -76,10 +74,9 @@ export default async function LessonEditorPage({ params }: Props) {
             published: lesson.published,
           }}
           courseId={courseId}
-          moduleId={moduleId}
           courseSlug={lesson.module.course.slug}
-          prevLesson={plain.siblings[idx - 1] ?? null}
-          nextLesson={plain.siblings[idx + 1] ?? null}
+          prevLesson={prevLesson}
+          nextLesson={nextLesson}
         />
       </div>