CDN-188: The Edge Moves Inward

CDN-188 resolves the high-xi theta40 grid-edge ambiguity left by CDN-186 and stressed in CDN-187. A wider fresh response-surface bracket for xi = 25.60 moves the theta40 signed peak inward from the old edge proxy 0.037339 to an interior log-quadratic peak at 0.035264. With this refined point, the high-xi theta20-to-theta50 peak history becomes strictly monotone and the fixed-floor four-point residual drops from 0.096147 to 0.008464. This stabilizes the high-xi peak-law branch while keeping D9 unpaid because the acoustic floor remains imported rather than internally derived.