Complex and Parametric Motion is still in progress

Start with complex numbers as points on one plane, then carry that same coordinate language into motion traced from x(t) and y(t).

This completion page stays public, but the completion reflection only unlocks after every concept and authored checkpoint in this track is clear on this browser. The route still reads the same local concept records and solved challenge ids, and signed-in sync keeps reusing those records instead of inventing a separate track store.