CDN-297: The Encounter Ledger

CDN-297 converts the CDN-296 signed-residual protocol into an intake ledger for future flyby-band encounter packets. The ledger defines the minimum evidence fields required before an encounter can enter the Channel-B regression: signed radial/tangential decomposition, residual sign convention, cleaned residual, covariance model, ordinary-systematics subtraction, kernel provenance, independent replay, and public packet completeness. A frozen twelve-case assay classifies packets as analysis-ready, null-control, quarantine, wall-tracer, or out-of-scope. Speed-only and sign-ambiguous claims do not count as clean GCFT dynamic evidence.