Certified critical-line bound 0.673600764507257397853295271394

By Samuel Lavery (github: samlavery) and his agent team (bridge-port, am-cert, mvt-engine, window-scope); Apache-2.0. Builds on our attempt-031. Window WL2 refines WL1 by our frame-LP window search (window declarations regenerated from its coefficients, ajp88's W9A2 structure credited in the file). New in the checker: every leaf may use the reflection half-space g0 <= g7 as an extra LP row (module PCellHalf), certifying straddling cells on one side only, which cuts the tree by about 16 %. Weights from our frame LP at full resolution; certified at margin 1.4e-5 (8,596 leaves) with splits at the LP minimiser, the fast leaf checker, an 8-unit tangent grid, range-end anchors and Yuhang Shi's anchor-variance term (PCellVarW, his notice kept). Exact maximal floor; H_W to 1e-40; long numerals use cafeai's zfNat64 packing.