CDN-377: The Analytic Residual Witness

CDN-377 removes the random-probe ambiguity from the finite-distance residual witness tested in CDN-375 and CDN-376. Using deterministic radial shells rather than a Monte Carlo cloud, the artifact measures the residual after subtracting the best local trace-free tensor fit and checks whether the result follows the expected Newtonian multipole powers. The fitted asymptotic slopes lock cleanly: axial_single = -1.000004, axial_binary = -2.000000, and planar_ring = -2.000000, with maximum absolute slope error 4.07e-6. The result shows that the residual scope witness is not a sampler artifact; it is an expansion-order signature, with single-node residuals scaling as H ~ D^-1 and symmetric hidden-domain residuals scaling as H ~ D^-2.