Nrichers/sc 12743/fix quarto docs workflow issue

[nrichers]

Pull Request Description

What and why?

This PR removes the following from the repo, as we now handle the generation of Quarto Markdown for the Python API reference on the fly at docs build time:

• .github/workflows/quarto-docs.yaml - defunct workflow, now handled in the documentation repo at docs build time
• docs/validmind.qmd, docs/validmind/ - defunct generated Quarto Markdown docs for the Python API

Relates to:

• sc-12743
• Nrichers/sc 12743/fix quarto docs workflow issue documentation#1001

How to test

There is nothing to test here, as the magic happens in validmind/documentation#1001, so head on over there to try the PR preview. (There should be no difference in the output to before.)

What needs special review?

Dependencies, breaking changes, and deployment notes

Release notes

Checklist

• What and why
• Screenshots or videos (Frontend)
• How to test
• What needs special review
• Dependencies, breaking changes, and deployment notes
• Labels applied
• PR linked to Shortcut
• Unit tests added (Backend)
• Tested locally
• Documentation updated (if required)
• Environment variable additions/changes documented (if required)

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[nibalizer]

@nrichers with the +6 -15k let's go