Certified critical-line bound 0.673638706661668668309739930008

By 贝奕 (Bei Yi). Derived from the attributed TEN ten-point certificate (Rishi Khan; Samuel Lavery, R. Arun Chandru et al.; Apache-2.0, all notices retained). An exact integer recomputation of all 27,554 leaf checks shows the floor c is not tight: c is raised from 78636809221179049927741289138/SA to 78636813132969021486827167078/SA (SA = 2^23*10^24), the largest value every leaf certifies (tightest leaf: root 54, walk position 10521). Certificate data (weights, lambdas, tangent table, pyramids, trees, multipliers) and all other proofs are unchanged.