What design features or systems help to prevent a hard nose landing?
The longitudinal stability of the aircraft.

Aircraft are designed so that at any given elevator position they maintain a corresponding angle of attack¹. Any decrease in AoA creates pitch up moment to increase it and vice versa.

At touch down the pitching moments change a bit, but the general tendency remains, so without change in the elevator position, the plane will tend to keep the nose wheel off the ground. The nose only touches down when the pilot eases the back pressure on the control column, or the plane slows down enough that the elevator efficiency decreases below what is needed to keep the attitude.

The pilot just has to ease the back pressure gently and not slam on the brakes until the nose wheel is on the ground, because brakes do generate significant downward pitching moment (this applies to all vehicles; you can feel it in a car quite well).



¹ except modern fighters, but there the control computer emulates that behaviour, otherwise they wouldn't be controllable.