Edit image with FLUX.1 Kontext [pro]

Submits an asynchronous image editing request using the FLUX.1 Kontext [pro] model. Accepts a base64-encoded input image and a text prompt describing the desired edit. The model uses contextual understanding to apply targeted edits while preserving the rest of the image. Returns a task ID for polling. Use cases include object replacement, background changes, style application, and detailed touch-ups.