chore: deprecate MkDocs docs

[andreatgretel]

Summary

Deprecates MkDocs as an active docs system on main now that Fern is the canonical Data Designer docs surface.

This PR does not modify the published gh-pages archive. The archive freeze and GitHub Pages redirect behavior were handled in merged PR #688, and gh-pages is now locked.

Changes

• Remove MkDocs source pages/assets, mkdocs.yml, and MkDocs-only docs workflows from main.
• Convert docs preview and devnotes publishing follow-up to Fern-only behavior.
• Drop MkDocs/mike/mkdocstrings docs dependencies and refresh uv.lock.
• Keep docs/ for Fern support inputs only: notebook sources, generated Colab notebooks, docs scripts, and downloadable recipe assets.
• Update current docs links to https://docs.nvidia.com/nemo/datadesigner.
• Keep the Fern redirect mapping for legacy MkDocs/devnotes URLs in fern/docs.yml.

Archive Boundary

• chore: deprecate MkDocs docs #687 targets main and stops new MkDocs builds from this branch.
• Merged docs: freeze gh-pages archive #688 targets gh-pages and freezes the GitHub Pages archive so only 0.5.7 and older remain available there.
• Merged docs: freeze gh-pages archive #688 also implements the latest, 0.6.0, 0.5.9, and 0.5.8 GitHub Pages redirects to Fern.

Attention Areas

• docs/ intentionally remains as a support directory for Fern-linked assets and notebooks.
• .github/workflows/docs-preview.yml now posts Fern previews only.
• fern/docs.yml remains the active Fern-side bridge for legacy MkDocs/devnotes paths.

Testing

• .venv/bin/ruff check --fix packages/data-designer/src/data_designer/interface/data_designer.py docs/notebook_source/*.py
• .venv/bin/ruff format packages/data-designer/src/data_designer/interface/data_designer.py docs/notebook_source/*.py
• make generate-colab-notebooks
• make check-fern-docs (fern check: 0 errors, 1 warning)
• git diff --check origin/main..HEAD
• CI passed on PR chore: deprecate MkDocs docs #687
• GitHub Pages archive/devnote redirects verified after docs: freeze gh-pages archive #688 merge
• Unit tests added/updated (N/A - no runtime logic changes)
• E2E tests added/updated (N/A - no runtime logic changes)

[github-actions]

Fern preview: https://nvidia-preview-pr-687.docs.buildwithfern.com/nemo/datadesigner

Fern previews include the docs-website version archive with PR changes synced into latest. Notebook tutorials are rendered without execution outputs in previews.

[johnnygreco]

Nice work on this cleanup, @andreatgretel — the MkDocs retirement boundary is much clearer now.

Summary

This PR removes the active MkDocs docs system from main, keeps Fern as the canonical docs surface, and updates the remaining repo guidance/links to point at docs.nvidia.com/nemo/datadesigner. The implementation matches the stated intent overall, but a couple of remaining docs/ support paths still need to be wired up so user-facing assets and docs preview coverage do not regress.

Findings

Warnings — Worth addressing

.github/workflows/docs-preview.yml:7 — Remaining Fern support assets no longer trigger docs preview

• What: The PR narrows the docs preview trigger from docs/** to only docs/notebook_source/** and docs/colab_notebooks/**, but docs/assets/recipes/** remains a supported input directory and is directly linked from many Fern recipe/devnote pages.
• Why: A PR that changes or breaks one of those downloadable recipe scripts will no longer run the Fern preview/check workflow, even though the published Fern pages still send users to those files.
• Suggestion: Add the remaining direct support inputs back to the path filter, at minimum:

      - "docs/assets/recipes/**"

  If changes under docs/scripts/** are expected to validate notebook/docs generation, I’d include that path as well.

docs/colab_notebooks/7-nemotron-personas.ipynb:29 — Nemotron Colab diagrams point at deleted assets

• What: The notebook still embeds three raw GitHub images from docs/devnotes/posts/assets/nemotron-personas/... at lines 29, 392, and 731, but this PR deletes that asset tree from main.
• Why: After merge, those raw.githubusercontent.com/.../main/docs/devnotes/... URLs will 404, so the user-facing Colab notebook linked from the Fern devnote loses its pipeline diagrams.
• Suggestion: Point the notebook at the surviving assets under fern/assets/nemotron-personas/, for example https://raw.githubusercontent.com/NVIDIA-NeMo/DataDesigner/main/fern/assets/nemotron-personas/nemotron_persona_via_ndd.png, and update the two step images the same way.

Suggestions — Take it or leave it

docs/scripts/generate_top_models_figure.py:52 — Top-model figure helper still recreates the removed docs/images path

• What: README.md now renders fern/images/top-models.png and this PR deletes docs/images/, but the helper still documents and writes docs/images/top-models.png as the canonical target before copying to Fern.
• Why: The next telemetry refresh will recreate docs/images/top-models.png as an untracked file, which makes the post-MkDocs ownership boundary fuzzy again.
• Suggestion: Make fern/images/top-models.png the sole or primary target, and update the docstring/comments so the script matches the new README image path.

What Looks Good

• The dependency cleanup is nicely scoped: MkDocs, mike, mkdocstrings-related packages, and the old Make target are removed without touching runtime package dependencies.
• The new docs/README.md is a helpful boundary marker for the remaining support files, especially now that docs/ no longer means “published prose.”
• The Fern preview workflow is simpler now that it no longer posts two separate preview systems, and the release/devnotes docs workflows keep the docs-website branch model intact.

Verdict

Needs changes — please address the docs preview trigger gap and the broken Nemotron Colab image URLs before merge. The top-model helper cleanup is optional, but it would keep the new docs ownership model tidy.

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This review was generated by an AI assistant.

[johnnygreco]

Approving per maintainer request. Please see my review comment for the warning-level follow-ups I found before merge.