IV.T164 — rho_bar = 1/(2*pi): omega-Period Structural Derivation (tau-effective)

Tau-effective: rho_bar = 1/(2*pi) = 0.15915 at +974.5 ppm from PDG rho_bar = 0.1590. Structural derivation: the omega-sector (Higgs mode) holonomy on tau^1 has period 2*pi in its phase coordinate. rho_bar is the fractional holonomy angle per generation step, normalized to [0,1]. Since the full period is 2*pi, the per-step fraction = 1/(2*pi). This directly connects the Wolfenstein CP parameter to the omega-sector crossing structure. Upgrades IV.P190 from proposition to theorem with structural derivation.