_ce_grad_gate_authored.nx

_ce_grad_gate_authored.nx -- the VERIFIED-GRADIENT gate for tg_celoss (op 6, fused softmax+cross-entropy), per the law established at T7: every op lands WITH its gradcheck. GATES: A gradcheck (analytic == central finite difference, all 5 logits, h=1/128, rel<1/32 floor 1/64) | B KAT uniform logits -> CE == ln(n) (the mathematical anchor, oracle = nx_f32_log itself on a DIFFERENT path: log(5) vs logsumexp of equal shifts) | C conservation (softmax - onehot sums to 0 => analytic grads sum to ~0). LAWS: flat ifs, no &&/||. license_tier: ORIGINAL