YouTube Short Scene Storyboard

Create a scene-by-scene storyboard from the approved YouTube Short script.

Treat the provided script as the single source of truth.

Requirements:
- Do not rewrite or paraphrase the script.
- Each scene narration must be an exact contiguous substring of the original script.
- Keep the narration in the same order and reproduce the full script when concatenated.
- Split the content into logical scenes based on changes in idea or visual concept.
- Total duration must equal the target duration exactly.
- Use visual types limited to: image, code, diagram, or text.
- Each scene should have one clear visual purpose and should explain the narration without relying on on-screen text.
- Keep visual instructions concrete and technically consistent with the narration.

Input:
- Script: [SCRIPT]
- Target duration: [30|45|60]

Return JSON in this format:
{
  "scenes": [
    {
      "id": "string",
      "durationSeconds": 5,
      "narration": "string",
      "onScreenText": "",
      "visualType": "image",
      "visualInstructions": "string"
    }
  ]
}