Create a webbook episode package for screenplay file `{source_file}`.

Use exactly `{web_episode_count}` webbook episodes.
Use exactly `{sections_per_episode}` image sections inside each webbook episode.
Write as long-form webbook prose, not a short summary.

Visual world guide:
{world_guide_json}

Screenplay text:
{screenplay_text}

Important extracted entities and relations:
{entities_json}

Scene still catalog:
{scene_stills_json}