CDN-259: The Two Sectors

Tests two-sector stitched κ model (CDN-242 logistic for clusters, CDN-258 power law for galaxies, sigmoid transition). Stitching provides NO improvement over raw galaxy-sector form (7/22 vs 8/22 within 20%). Residual scatter (σ = 0.43) is irreducible without per-system dynamical modelling — driven by orbital anisotropy, tidal disruption, binary contamination, and non-equilibrium. M/L corroboration: 5/22 within 30%. Acceleration-only ceiling reached at ~35% success rate. D9 three-quarters paid.