nx_tstp_emit.nx

nx_tstp_emit.nx -- TSTP-format proof serializer. Walks the ProofLog + clause set and emits the proof in TSTP format: cnf(c0, axiom, p(a)). cnf(c1, axiom, ~p(a)). cnf(c2, plain, $false, inference(resolution, [], [c0, c1])). Required for CASC submission output. Closes the substrate-side of the BLOCKED_ON_PROOF_HISTORY_TRACKING axis once integrated with the saturation loop (this commit ships the standalone serializer; loop integration is a follow-up). Output discipline: each clause emitted exactly once in proof order (transitive ancestors of the empty clause first, then the empty derivation last). The caller can pre-walk via nx_proof_walk_ancestors to determine the minimal proof support.