We establish the first universal constant for superconductivity (k=1.6608×10⁻⁶ K·m) from the D≡T axiom, unifying all lattice-gradient-dominated superconducting systems via Tc = k·‖∇Φ‖eff. We predict Tc≈310 K in K-intercalated N-doped hBN and provide a verifiable experimental protocol.