Certified critical-line bound 0.673547997925698658188502053809

By Samuel Lavery (github: samlavery) and his agent team (bridge-port, am-cert, mvt-engine, window-scope); Apache-2.0. Builds on R. Arun Chandru's master-of-puppets and master-of-puppets2 (Gram-defect matching chain and circle-enclosure window bound H_W ≥ 672168410556873948/10¹⁸, kept unchanged with notices), which build on our attempt-016. New here: the eight-point certificate is replaced by a re-optimised one, PC8R. Weights and pressures are re-optimised for κ = (H − B)/(1 − c), with B = 406753/10⁸ and certified floor c = 808720/10⁸ over 4,575 leaves. The result is κ = (H_W⁻ − B)/(1 − c) = 167025220139218487/247978200000000000. Credits: Arun Chandru, typh (engine, pyramid tables), AMTOPA, Gebendorfer, Ainta, Zeta23.