Validate brain extraction / skull stripping results. Generate a QC PNG mosaic, perform AI visual evaluation against a structured rubric, and produce a matching human verification form for reliability comparison. Invoke after brain extraction completes, or standalone on any existing brain mask with "check brain extraction", "QC the mask", "validate skull strip", "review brain extraction", "evaluate the mask", or "brain-extraction-qc". Also invoke when the user references a file ending in `_brain.nii.gz`, `_mask.nii.gz`, or `_brain_mask.nii.gz` and asks to check, review, or validate it.
