PUH Theorem 295 (Derivation, Calibration, and Bracket) — The Cascade Endgame: Snap Ignition at the Interior Threshold Φ* = 1/128; the Freeze Exponent as a Volume-Vanishing Exponent Calibrated on Five Instances; the Quaternionic Bracket p ∈ 6, 19 from E8(−24) Nilpotent Data | Synapse