xAI: Grok Imagine Image 2.0 API

grok-imagine-image-2.0 is xAI's recommended image generation and editing model. It supports text-to-image and image editing with up to five source images (reference them positionally as <IMAGE_0>, <IMAGE_1> in the prompt), 1K / 1.5K / 2K output and low / medium quality. When quality is omitted, xAI picks it automatically (currently low for generation and medium for editing) and bills the tier actually served.