chore: Ensure null validation for private attribute in messages (#8085)

enterprise/app/models/response.rb

@@ -6,7 +6,7 @@
 #  answer               :text             not null
 #  embedding            :vector(1536)
 #  question             :string           not null
-#  status               :integer          default(0)
+#  status               :integer          default("pending")
 #  created_at           :datetime         not null
 #  updated_at           :datetime         not null
 #  account_id           :bigint           not null