nx_ppmi_lib_gate.nx

nx_ppmi_lib_gate.nx -- KAT + neg-controls for the shared PPMI library (seq283) and its new IDF weighting. Proves: the path-parameterised loader works, informativeness weighting really does rank a ubiquitous function word below a discriminative one, out-of-vocabulary terms are EXCLUDED from the weighted denominator instead of dragging a flat mean toward zero, and the weighted scorer still agrees with the flat one where no weighting distinction exists. Runs from the nxc2 CWD so knowledge/index/semppmi_v1.bin resolves. DRY nx_gate_verdict lib.