Fix saveLesson: sanitize content JSON to prevent RSC proxy error

React treats TipTap's editor.getJSON() output as a non-plain object when
passed through Server Action serialization, causing isDecimal() inside
Prisma's query builder to receive a temporary client reference proxy and
throw ERROR 1213974697. JSON.parse(JSON.stringify()) strips the prototype
chain and any non-enumerable properties, ensuring Prisma receives a
clean plain object.

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

src/lib/actions/lesson-actions.ts

@@ -22,7 +22,6 @@ export async function saveLesson(
   }
 ) {
   await requireAdmin();
-  try {
   await prisma.lesson.update({
     where: { id: lessonId },
     data: {
@@ -32,10 +31,6 @@ export async function saveLesson(
       published: data.published,
     },
   });
-  } catch (err) {
-    console.error("[saveLesson] full error:", err);
-    throw err;
-  }
   revalidatePath(`/admin/courses/${courseId}/modules/${moduleId}`);
   revalidatePath(`/admin/courses/${courseId}/modules/${moduleId}/lessons/${lessonId}`);
 }