Gravity and Orbits is still in progress

Start with one source mass creating a field and potential well, then use that same gravity model to explain circular speed, orbital periods, and the escape threshold.

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.