How do cross-wind correction controls help while on the ground with wings level?
Your assumption is that the wings are level when both main wheels are on the ground. But this is not necessarily true. Even when both wheels are on the ground, the wings can still have a small tilt. The suspension of each gear works independent of the other, and the weight on the wheel determines how much the suspension compresses or the gear strut will bend. By deflecting the ailerons, you re-distribute the lift between the wings, and control gear compression.

Please note that with the ailerons level, your wing will create a sizable rolling moment in a crosswind, which means that the load distribution between the two main wheels is uneven without aileron correction. Also, the fuselage will create a side force of its own, and this force increases with speed as more of the flow around the fuselage will be attached.

The slight tilt angle of the wing also slightly tilts the lift vector, and this, together with the side force of the fuselage, creates the side force which causes the skidding when this side force is large in comparison with the low load on the wheels shortly before takeoff. You need to tilt the wing into the crosswind to create a counter-force which can compensate the side force of the fuselage, only then the whole aircraft will not experience a side force.

I know, the picture below shows a glider and not a Citabria, but the principle is the same. The high wing arrangement creates a sizable rolling moment even without dihedral.