refactor: some renaming and corrections

prisma/schema.prisma

@@ -14,8 +14,8 @@ model User {
   code      String   @unique
   confirmed Boolean  @default(false)
   deleted   Boolean  @default(false)
-  createdAt DateTime @default(now()) @map(name: "created_at")
-  lastMail DateTime @default(now()) @updatedAt @map(name: "updated_at")
+  createdAt DateTime @default(now())
+  lastMail  DateTime?
 
   @@map(name: "users")
 }