A 58-year-old woman presents with a intensely itchy rash on her wrists and ankles. On examination, there are multiple small, violaceous, polygonal, flat-topped papules. There are also fine white lines visible on the surface of some lesions (Wickham's striae). She also mentions soreness in her mouth, and examination reveals white lace-like lesions on the buccal mucosa. What is the most likely diagnosis?