IV.R400 — PMNS CP Phase δ_CP from σ-Breaking; New OQ-C6/C7

PMNS CP phase δ_CP and Majorana phases arise from σ-symmetry breaking by A-sector flavor rotation. Connection to IV.T146 (Majorana from σ=C_τ): Majorana phases are additional CP phases beyond δ_CP, all constrained by σ-equivariance. New open questions: OQ-C6 (ρ̄=1/(2π) structural derivation), OQ-C7 (A-sector PMNS rotation).