A 38-year-old man presents to the emergency department with acute left flank pain radiating to the groin, associated with nausea and vomiting for the past 6 hours. He has a history of recurrent kidney stones. On examination, he is restless, with costovertebral angle (CVA) tenderness on the left side. Vital signs are stable. Non-contrast CT (NCCT) abdomen shows a 6 mm stone in the left ureter at the level of the pelvic brim with mild hydronephrosis. Serum creatinine is 1.0 mg/dL, and urinalysis shows hematuria. What is the most appropriate initial management?