Build against the Splat3D API (https://api.splat-3d.com). Read
https://docs.splat-3d.com/llms-full.txt first.

- Auth: Authorization: Bearer s3d_..., read from an env var on the server.
  Never put the key in a browser, app bundle or repo.
- Loop: POST /v1/scenes {content_type, file_size} -> PUT the file to
  data.uploadUrl with the same Content-Type -> POST /v1/scenes/{id}/process
  -> poll GET /v1/scenes/{id} every 5-10 s until status is complete, failed
  or cancelled -> GET /v1/scenes/{id}/download?format=sog|ply|spz.
- /process charges once per scene. Repeat it only with the same body (a
  different one is 409). Never create a new scene to retry.
- Errors: {error: {code, message, details?}, meta: {request_id}}. On 429
  queue_full, wait Retry-After seconds and call /process again. On 429
  rate_limited (300 requests or 30 launches a minute per account), wait
  Retry-After seconds and repeat the request. Retry a 503 only when it
  carries Retry-After.
- Inputs: a video of 30+ seconds, a zip of 20+ JPEG/PNG photos taken all
  around the subject, a COLMAP workspace zip, or a SplatKing export zip as
  exported: https://docs.splat-3d.com/guides/supported-inputs