A 42-year-old man with advanced HIV/AIDS (CD4 count 45 cells/μL) presents with white plaques on his tongue and oral mucosa that cannot be scraped off easily. He also reports dysphagia and retrosternal chest pain. Endoscopy shows white plaques extending into the oesophagus. KOH mount of a biopsy specimen shows budding yeast and pseudohyphae. Culture grows white, creamy colonies on Sabouraud dextrose agar. The isolate produces germ tubes in human serum at 37°C and forms chlamydospores on cornmeal agar. What is the most appropriate first-line antifungal therapy for oesophageal candidiasis in this patient?