A former Santander Bank employee in Rhode Island has pleaded guilty in federal court to charges related to stealing more than $125,000 from the bank account of a 78-year-old customer with dementia.Carlos Bras, 41, of East Providence, appeared in federal court where he admitted to mail fraud and aggravated identity theft, the Justice Department said Wednesday. At the time of the theft, Bras was working for the Spain-based global financial institu…