Build an AI workout plan generator with progress tracking. Features: 1) Onboarding quiz: goal (strength, hypertrophy, fat loss, endurance), experience level, available equipment, days per week, injuries and limitations. 2) AI-generated weekly plan with sets, reps, rest, and progression notes, regenerated whenever the user changes constraints. 3) A video or animated demo link for every exercise, with a substitutions option for missing equipment. 4) A workout logger with set-by-set tracking, rest timers, and a checkoff flow that works one-handed at the gym. 5) Progressive overload logic that bumps weights or reps next week based on logged performance. 6) A deload and fatigue flag when the user logs several missed or failed sessions. 7) Simple charts for volume and consistency over time. 8) No food tracking required, but allow optional bodyweight and measurement logging.