Check retractions, duplicates, and a second extractor's values

Check retractions, duplicates, and a second extractor's values

Query retraction and correction notices for every included trial, detect duplicate publications of the same cohort, and have a second extractor redo the numeric fields blind to the first. Deliverable: A checked evidence table with retraction_status and duplicate_group, plus a disagreement log. It is an evidence audit, not treatment advice.