AI IMAGE GENERATION — POST {prompt} and get back a PNG, base64 in JSON (?raw=1 for raw bytes). Gemini 2.5 Flash Image (nano-banana): photoreal scenes, illustrations, product shots, UI mockups — renders text in images well. Optional {aspect_ratio}: 1:1 (default), 16:9, 9:16, 4:3 + 6 more. Reference images: pass {url} or {image_base64}, or up to 3 in {reference_images}, to edit, restyle, or compose