Oscillations and Energy is still in progress

Build from one clean oscillator to energy exchange and then to driven resonance, so the same system grows without changing its core ideas.

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.