add constraints for member-user and member-property

lib/accounts/user.ex

@@ -12,6 +12,12 @@ defmodule Mv.Accounts.User do
   postgres do
     table "users"
     repo Mv.Repo
+
+    references do
+      # When a member is deleted, set the user's member_id to NULL
+      # This allows users to continue existing even if their linked member is removed
+      reference :member, on_delete: :nilify
+    end
   end
 
   @doc """