Generate an image with optional brand style and subject compositing.
If style_id is provided, loads the image style for brand-consistent generation.
If brand_subject_id is provided, loads subject context for compositing.
API key prefixed with cr_ (e.g. cr_a1b2c3...)
Image style for brand-consistent generation
16:9, 9:16, 1:1, 4:3, 3:2, 4:5, 21:9 standard, high Brand subject for compositing