There is no need to immediately change your workflow if the PHP converter is working for you.
That being said, I have just finished publishing the converter as a proper NPM module, so you should be able to install and use it as follows. You will need to have a relatively recent version of Node.js installed for this to work.
npm install -g lv_img_conv
npx lv_img_conv --help
npx lv_img_conv logo_lvgl.png -o myfile.c -c CF_TRUE_COLOR_ALPHA # convert logo_lvgl.png to myfile.c with true color alpha format
The help option lists all the possible color formats.
You should be able to adapt the last command to a shell script easily.