What is the ruling on the prayer of someone afflicted with obsessive-compulsive disorder who, due to it, pronounces the takbīrat al-intiqāl (takbir of transition) before moving in prayer? And how can one balance adherence to the Sharia with not succumbing to the obsessive whispers after recovery from it?

You should not have cut off the prayer because of intrusive thoughts (waswas (definition)). The cure for intrusive thoughts is to disregard them and pay no attention to them, even if Satan deludes you into thinking that doing so is an application of fiqh. The transitional takbirat (saying "Allahu Akbar" when moving between prayer postures) are recommended by the majority of scholars, and omitting them or performing them out of place does not invalidate the prayer. There is no harm in adopting the easier opinion among the sayings of the jurists to ward off intrusive thoughts.