Make thumbnails for YouTube clips

A webhook starts it from a row in your YouTube clips table. It reads the clip, its parent session and a reference thumbnail, creates a placeholder row in your creatives table and splits the clip's thumbnail titles into one item per title.

For each title it builds an image prompt from the reference image and the host or guest headshot, depending on the layout. A switch sends the request to one of three Fal.ai request shapes for the chosen model, and the workflow polls until each image is ready. The images are attached to the creative row, which is set to To Do, and costs are logged. The clip rows come from the Plan YouTube clips workflow.