“The government has put Mr. Hamdi in a legal purgatory. If he were charged with a crime in a civilian court, as Zacarias Moussaoui, the alleged 20th hijacker, was, he would have access to a lawyer and due process rights. If he were a prisoner of war, the Geneva Convention would guarantee him other significant rights. Instead, the administration has employed this third category — enemy combatant — and says that it carries none of those protections.”