A 36-year-old woman, a recently promoted senior manager, presents seeking evaluation for concentration difficulties that she attributes to work stress. She reports chronic difficulty with organization, time management, and task completion that she has 'always compensated for' using extensive lists, alarms, and rigid routines. Since her promotion 4 months ago, her compensatory strategies have become insufficient, and she is struggling significantly. On detailed history, she describes always being a 'daydreamer' in school, frequently losing belongings, difficulty sustaining attention during meetings, often starting tasks but not finishing them, and chronic difficulty with punctuality. She was an academically gifted student who 'could have done better' and was frequently told she was 'not working up to her potential.' She reports no hyperactivity but endorses internal restlessness and frequent shifting between tasks. She has no history of mood disorders, anxiety disorders, or substance use. Her mother confirms the patient has exhibited these patterns since early elementary school, describing her as 'smart but scattered.' Neuropsychological testing reveals deficits in sustained attention and executive function with a superior IQ. Which of the following is the most likely diagnosis?