- Remove fixed 0-4095 mapping, use cal_min/cal_max instead
- Auto-calibrate minimum at boot (assumes pedal at heel)
- 'cal min' sets current position as heel (0)
- 'cal max' sets current position as toe (127)
- Map cal_min->0, cal_max->127 with clamping
- Update 'exp' command to show raw ADC + cal values