The horrific Inwood fire that killed three people, including a top veteran fashion journalist and her elderly mother, was caused by a neighbor who carelessly flicked his cigarette butt, prosecutors said Tuesday. The tragic detail was revealed as suspect Victor Arias, 29, was arraigned in Manhattan court on three counts of criminally negligent homicide for the May 4 inferno — then freed on supervised release. Victor Arias, 29, allegeldy carelessly flicked hs still-smoldering cigarette butt on some cardboard boxes, igniting an Upper Manhattan fire that killed three people earlier this month. Steven Hirsch for NY Post The fire soared through the building to its upper floors.…