nx_etg_tournament_test.nx

nx_etg_tournament_test.nx -- KAT for E2 tournament selector. Verifies: T1 All-correct variants: winner = argmin(perf_metric). T2 Mixed correct + failed: failed variants ignored even if they have lower perf; winner is correct + argmin. T3 All variants failed: returns NX_ETG_TVAL_NO_WINNER; never silently picks a failed variant. T4 Tie-break determinism: equal perf -> earlier variant wins. T5 N=0: returns NX_ETG_TVAL_NO_WINNER (no underflow). T6 N=1 correct: that variant wins regardless of its perf. T7 N=1 failed: returns NX_ETG_TVAL_NO_WINNER. T8 Attestation emits a valid E1 entry with outcome=RECLAIMED + claim_source=PRIOR_CALIBRATION + claim_value=variants_tested + measurement_value=winning_variant_id + reclamation_delta=1.