Scalar preview: replace deprecated 'hideDownloadButton' with 'documentDownloadType: "none"'

[char0n]

Where it shows up

Every time the API preview opens, Scalar logs:

  @scalar/api-reference@1.44.15
  [DEPRECATED] You're using the deprecated 'hideDownloadButton' attribute.
  Use 'documentDownloadType: "none"' instead.
  Document  not found in configList

Suggested fix

In the Scalar configuration the preview command passes to @scalar/api-reference,
swap the attribute:

  -  hideDownloadButton: true
  +  documentDownloadType: 'none'

The Document not found in configList line (note the double space — empty
document name) usually indicates the preview is initialized before the document
is added to Scalar's configList. Worth re-checking the init order so the
default document isn't asked about during the warm-up frame.

Repro

Open any OpenAPI spec in https://github.com/speclynx/speclynx-editor; the warning
fires on every preview render.