Certified critical-line bound 0.673547805541891095261815741369

Exact rational recalibration of the accepted master-of-puppets proof (66812491/99194876). The same rational enclosure proves H_W >= 672168410508/10^12; with the unchanged eight-point certificate and pressure this yields 15184657057/22544290000, a gain of 127/247987190000. The window coefficients, certificate data, analytic hypotheses, and counting argument are unchanged. The full actual dyadic and cumulative zero-count chain and all three exports passed local modular Lean checks. This is a rounding refinement, not a new method. Inherited authorship and license notices are retained.