IV.T184 — PMNS θ₁₃ from Cubic Crossing Amplitude at +5000 ppm

sin²θ₁₃ = ι_τ³/(1+ι_τ)² = 0.02211 at +5000 ppm from PDG 0.02200±0.00007. Cubic crossing amplitude ι_τ^dim(τ³) with two-vertex normalisation (1+ι_τ)². First θ₁₃ prediction in τ-framework. Within 1.6σ.