Thousands of displaced Palestinians poured back into the shattered north of Gaza on Friday, trekking through wastelands and rubble to the ruins of homes they had not seen in two years, as a ceasefire took effect and Israeli troops began withdrawing under the first phase of a US-brokered peace deal.Long columns of families, many barefoot or pushing bicycles laden with salvaged belongings, walked along Gaza’s coastal highway toward Gaza City, the enclave’s largest urban center and the site of one of Israel’s fiercest offensives. To the south, residents picked their way through the pulverized remains of Khan Younis, once Gaza’s second-largest city, now reduced to dust and twisted metal.