BUENOS AIRES, Argentina (AP) — Thousands marched through Buenos Aires on Tuesday to mark 50 years since the 1976 military coup that ushered in one of Latin America’s bloodiest dictatorships. An estimated 30,000 people were disappeared by the regime in its campaign against dissents, including a left-wing guerrilla movement, labor activists and students, according to human rights organizations. Official figures place the number at around 8,000. A truth commission and human rights groups attribute