calendar add created at

prisma/schema.prisma

@@ -51,6 +51,7 @@ model Event {
 }
 
 model Calendar {
-  slug    String    @id @default(cuid())
-  lecture Lecture[]
+  slug      String    @id @default(cuid())
+  createdAt DateTime  @default(now())
+  lecture   Lecture[]
 }