Reuses the pinned Re100 runner and helpers unchanged; sets only the
lattice viscosity for Re 20. Reports Cd, Cl and p_diff (dp * 0.04 for
U = 0.2 m/s), a steady rule frozen before any run (window ranges at most
a tenth of each official interval width) and no interval verdict when
not steady. Declares the pressure-NEQ outlet and Zou-He inlet deviations.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit 9b8ff90609)