DataDesigner

Maintain the NeMo Data Designer Fern docs site under fern/. Use for any documentation change. Triggered by: "edit docs", "add doc page", "update docs", "rename page", "fix broken link", "add redirect", "preview docs", "publish docs", "regenerate notebooks", "update dev note", any request that touches `fern/`.

Perform a thorough code review of the current branch or a GitHub PR by number.