A 28-year-old woman involved in a rollover accident presents with severe abdominal pain, tachycardia (HR 118/min), and hypotension (BP 88/54 mmHg). On examination, she has bruising over the left flank and left upper quadrant tenderness. Two large-bore IVs are established and fluid resuscitation initiated. What is the most appropriate investigation of choice to detect intra-abdominal bleeding and guide management decisions in this hemodynamically unstable patient?