Truth be told, while I had known about ESPHome while working on this project, for some reason, I just felt the urge to hack together my own firmware.
It might've been because my early testing was done via an old Arduino Uno board, and I must've figured that I might as well port the sketch over to the ESP32 once I had it working.
(I'm general though, I will say that LLMs can totally write bespoke one-off firmwares like this, and I don't feel too bad about it, given that it's running entirely within my LAN, and will never actually get "productized")
It even has a component specifically for the ULN2003 stepper motor driver you were using
https://esphome.io/components/stepper/#uln2003-component