Prevent accidental serialization of Account and User records (mas…

…todon#30079)

app/models/application_record.rb

@@ -22,4 +22,10 @@ def boolean_with_default(key, default_value)
       value
     end
   end
+
+  # Prevent implicit serialization in ActiveModel::Serializer or other code paths.
+  # This is a hardening step to avoid accidental leaking of attributes.
+  def as_json
+    raise NotImplementedError
+  end
 end