Add course tree, lesson actions, and module description schema

- CourseTree: expandable module/lesson overview with Eye/Video icons
- SortableLessons: Kinescope ID in create form, published toggle, move-to-module dropdown
- Actions: toggleLessonPublished, moveLessonToModule, updateModule with description
- Schema: add description field to Module model + migration

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

prisma/schema.prisma

@@ -108,12 +108,13 @@ model Course {
 }
 
 model Module {
-  id        String   @id @default(cuid())
-  courseId  String
-  title     String
-  order     Int      @default(0)
-  createdAt DateTime @default(now())
-  updatedAt DateTime @updatedAt
+  id          String   @id @default(cuid())
+  courseId    String
+  title       String
+  description String?
+  order       Int      @default(0)
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
 
   course  Course   @relation(fields: [courseId], references: [id], onDelete: Cascade)
   lessons Lesson[]