docs(mesh): sweep for ClusterClient deletion — Dps|Grpc only, CentralContactPoints retired

Task 3.2 of the ClusterClient->gRPC migration. Sweeps the docs that still
described the Akka ClusterClient transport as live, following its Phase 3
deletion (this branch): MeshTransport:Mode is now Dps (pair-local DPS) or
Grpc (cross-mesh unary calls) only, ClusterClient fails validation loudly,
CentralContactPoints is deleted (not superseded), and the split-topology
validator requires exactly Grpc rather than ClusterClient.

- docs/Configuration.md: rewrite the MeshTransport section — table,
  dark-switch/PSK-seeding prose, listener sharing (:4056 driver-role,
  :4055 admin-role), remove the "shipped dark, cutover pending" framing.
- docs/Redundancy.md: replace the Dps/ClusterClient transport table with
  Dps/Grpc, fix the Phase 6 CentralCommunicationActor + validator bullets.
- docs/Telemetry.md: fix stale ClusterClient cross-refs, add a note that
  the driver-role telemetry listener also hosts NodeCommandService.
- docs/v2/config-db-schema.md: one-line "(retired: ...)" annotation on the
  historical AkkaPort/GrpcPort note — left as a historical record otherwise.
- CLAUDE.md: rewrite "## Mesh command transport (MeshTransport)" for the
  post-deletion world (no ClusterClient/receptionist, per-node gRPC dial,
  fire-and-forget semantics unchanged) and fix two Phase 6 bullets.

deferment.md has no mesh-transport mentions; left untouched.

docs-only change; `dotnet build ZB.MOM.WW.OtOpcUa.slnx` stays green (0
errors) after the edit.

Claude-Session: https://claude.ai/code/session_014WNM4vjoVksyyBraTXSZE1

docs/v2/config-db-schema.md

@@ -177,7 +177,11 @@ from `Cluster:Port` in its own appsettings; these columns duplicate that value f
 cannot see the node's config. Today central shares a gossip ring with every node and does not need
 them — [per-cluster mesh Phase 2](../plans/2026-07-21-per-cluster-mesh-design.md) splits the fleet
 into one mesh per `Cluster`, after which `Host` + `AkkaPort` is how central builds its ClusterClient
-contact points, and `GrpcPort` is the Phase 5 telemetry stream.
+contact points (**retired**: the Akka `ClusterClient` transport was deleted by the
+[ClusterClient→gRPC migration](../plans/2026-08-06-clusterclient-to-grpc-design.md) — central now
+dials `NodeCommandService` at `Host`+`GrpcPort` instead, and `AkkaPort` is Akka remoting only), and
+`GrpcPort` is the Phase 5 telemetry stream **and**, since that migration, the Phase 2 gRPC command
+dial target too — see [`Configuration.md` § `MeshTransport`](../Configuration.md#meshtransport-centralnode-command-transport).
 
 `AkkaPort` is `NOT NULL DEFAULT 4053` because every node listens on a remoting port — `0` is never a
 truthful value, and rows predating the column must migrate to something real. `GrpcPort` is nullable