PESHAWAR, Pakistan — Hundreds of thousands of undocumented Afghan migrants are facing deportation from Pakistan to the Taliban-ruled country that some of them have never even visited. In a surprise announcement last month, the Pakistani government said it would arrest and deport an estimated 1.7 million unregistered or undocumented foreigners starting Nov. 1. Though Pakistan says the crackdown is not aimed at any particular nationality, most of the foreigners living there are from neighboring...