Is it permissible to pray for vengeance against one who wronged me, so that I may be treated justly, or is prayer restricted to seeking justice from Allah, who takes charge of the oppressor's affair?

Praying for people's guidance is a Prophetic Sunnah (definition), just as the Prophet, peace and blessings be upon him, prayed for Daws and Thaqeef. As for praying against an oppressor, it is permissible, but forgiveness and patience are better, for Allah Almighty says: "And whoever is patient and forgives, indeed, that is of the matters [requiring] determination." (Quran 42:43) Allah has permitted the wronged person to supplicate, by His saying: "Allah does not like the public mention of evil except by one who has been wronged." (Quran 4:148) Among the legitimate supplications established in the Sunnah are: "And grant me victory over whoever has oppressed me, and show me my revenge on him," and "And make our revenge against whoever has wronged us, and grant us victory over whoever has shown enmity towards us." It is permissible to supplicate against the oppressor that Allah may do justice to you against him, provided that the supplication does not exceed the extent of the injustice.