add some comments

priv/repo/migrations/20250926180341_add_unique_email_to_members.exs

@@ -8,6 +8,8 @@ defmodule Mv.Repo.Migrations.AddUniqueEmailToMembers do
   use Ecto.Migration
 
   def up do
+    # Ensure email uniqueness across all members
+    # This supports upsert operations and prevents duplicate member accounts
     create unique_index(:members, [:email], name: "members_unique_email_index")
   end