Visual Transformation Builder — rename protection for downstream datasets

The Visual Transformation Builder now protects you from silently breaking downstream datasets when you rename a parent column. On save, if a renamed column has dependent SQL-transform datasets, you'll see a "Dependent datasets affected" confirmation that lists the affected dependents and lets you cancel or save anyway. Affected child datasets are automatically flagged and self-heal once re-saved, and the dataset lineage view now shows an amber "upstream column renames" warning (with the old-to-new column names) so the impact is visible at a glance. As part of the same update, column renames now propagate correctly through to report and export headers and downstream SQL aliases.

This is a forward-looking protection only: existing or previous renames are not backfilled. No configuration or migration is required; it is live for everyone.