f1ad967083
Complete executable plan: PSK-from-Secrets auth (Phase 0), central_control + site_command proto contracts behind transport seams inside the two communication actors (1A ∥ 1B in worktrees), per-direction cutover flags, ClusterClient/receptionist deletion, 8-check live gate. Design doc: scadaproj/scadabridge_clusterclient_to_grpc.md (§7 = deep-dive corrections).