How can the Hadith "Nothing interrupts prayer, so ward off as much as you can" be reconciled with the Hadith "If one of you prays towards something that screens him from people... he should fight him, for he is but a devil"?

There is no contradiction between the two hadiths; they both agree on the command to repel the one passing in front of a worshipper, and that this passerby is a devil. So, "ward off what you can" is a command to resist and fight him if he refuses to move. The meaning of the passerby being a devil is that Satan incited him to pass, or that he acts like a devil, or that what is meant is the Qareen (companion jinn). The first hadith adds that nothing interrupts the prayer.