GCFT-0440: The Coherence Kernel — Action-Admissible C[Xi] Instantiation and the Positive Correlation Gate

GCFT-0440 instantiates the GCFT-0439 constraint-manifold scaffold as a frozen, action-admissible coherence functional. It defines a positive, phase-blind kernel ansatz for C_mu[Xi], proves local positivity and phase-blindness certificates, and shows how correlation content can move configurations across the manifold access gate. The endpoint remains sealed: the BRST operator basis, finite broken-phase matching, and scale-stability checks remain open.