V.T180 — (5/6) Uniquely Forced from Threshold Topology

(5/6) uniquely forced: 6 canonical thresholds, exactly 1 resonant (L_B, ω-crossing singularity), 5 non-resonant. ω = γ∩η is the unique self-coupling singularity of L. Cross-check: (5/6)·(8/27) = 20/81 = Y_p. Wave 11 upgrade: threshold uniqueness proof establishes (5/6) is not an identification but a forced consequence of ladder topology.