Create Story

Creates a story row for the user.

stories columns: id, name, description, file_url, created_at, duration, status, user_id, characters, thumbnail_url Storage path: {user_id}/stories/{story_id}.mp4 Thumbnail path: {user_id}/stories/{story_id}/cover.png

onboarding_theme_key: queue the user's FREE onboarding first story. Either one of the 4 static 30s adventure templates (pirate_treasure / space_mission / dino_discovery / ocean_quest), or the "custom" sentinel, where the parent wrote the lesson themselves during onboarding and description carries it (no template — it runs the normal custom pipeline at 30s). Both routes are server-guarded the same way: once per user ever, zero star cost.