Provider-specific fields

Each experimental provider adds style and asset fields of its own, under providerOptions.<provider> on the style and providerInputs on the asset. They are documented with the provider:

• Retro Diffusion: still styles, tilesets, and GIF or spritesheet animation.
• ComfyUI: a committed workflow, its bindings, revisions, and atomic frame sets.
• Scenario: hosted model ids and Compute Unit ceilings.