Exact-pin elliptic-curve audit aggregate

This root makes the retained elliptic-curve reduction cone and its integration harness available as an explicit CI and release-audit target. It is not a default Lake target or a curated public facade. Downstream modules should import the narrow EllipticCurves.* module that owns the required API; the compatibility public import in EllipticCurves.VariableChange is an explicit exception. The source exposition scans these files independently of this aggregate.

PORTING.md is the authoritative source-to-destination manifest and records which files are retained ports, exact-pin adaptations, compatibility modules, or project-owned harnesses.