A 55-year-old woman with a history of peptic ulcer disease presents to the emergency department with sudden onset severe epigastric pain radiating to the right shoulder. She appears acutely ill and is in severe distress. Vital signs show BP 110/70 mmHg, HR 110/min, RR 22/min. On examination, her abdomen is rigid with severe guarding and rebound tenderness. An upright chest radiograph is obtained as part of the acute abdomen workup. What is the most likely radiological finding on the upright chest X-ray?