WASHINGTON — Eighty-three victims and family members in the worst-ever mass shooting at a U.S. military installation are seeking $750 million in compensation from the Army, alleging that willful negligence enabled psychiatrist Maj. Nidal Hasan to carry out a terrorist attack at Fort Hood, Texas. The administrative claims filed last week said the government had clear warnings that Hasan, who is scheduled to go on trial in March, posed a grave danger to the lives of soldiers and civilians.