nx_atm_trans_gate.nx

nx_atm_trans_gate.nx -- GATE for the nx_atmosphere transmittance rung (2026-08-26). Accept rule, PRE-DECLARED (before the lib compiled): the i64 march must reproduce the 20,000-sample double-precision reference (computed from the same [bytes] medium table, knowledge/library/sky_volumetrics_impl_spec_2026-08-26.md) within +-64 q16 at four KAT angles; expneg must match exp() KATs; ozone tent endpoints exact; transmittance monotone in mu; and a single-species control must DIVERGE from the KATs, proving they discriminate the full medium. license_tier: ORIGINAL No hw writes (Rule 26).