image_generation creates an image-generation job through wp-ai-client, then sideloads the result as WordPress media.

Inputs

• prompt: detailed image prompt.
• provider: optional wp-ai-client provider override.
• model: optional image model override.
• aspect_ratio: 1:1, 3:4, 4:3, 9:16, or 16:9.

Default aspect ratio is 3:4 for portrait blog/Pinterest images.