docs(mesh): Phase 6 — mark done, remove single-mesh caveats, document pair-local meshes

Redundancy.md: KNOWN-LIMITATION (per-Akka-cluster election) marked RESOLVED;
new 'Per-cluster meshes (Phase 6)' section + pair-local secrets note; manual-
failover mesh-scope caveat removed; auto-down 1-vs-1 note updated (every mesh is
now two nodes, drill deferred to Phase 7). IManualFailoverService + ClusterRedundancy
razor caveats updated to pair-local reality. Configuration.md documents the
cluster-{ClusterId} role, per-pair self-first seeds, SplitTopologyTransportValidator,
and the intentional Dps default. Program + design status tables + CLAUDE.md marked
Phase 6 DONE.

(Task 8 subagent completed the edits but died on an API error before committing;
reviewed and committed by the controller.)

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW

docs/plans/2026-07-21-per-cluster-mesh-design.md

@@ -312,7 +312,7 @@ Deliberately not a task plan — per-phase plans follow, one at a time.
 | 3 | Config fetch-and-cache: artifact served by central, driver nodes read LocalDb (§6.1) | No |
 | 4 | Cut the driver-side ConfigDb connection: re-home `EfAlarmConditionStateStore`, resolve the `DbHealthProbeActor` ServiceLevel input, audit `OpcUaPublishActor` | No |
 | 5 | gRPC stream contract; migrate the seven observability topics | No |
-| 6 | Mesh partition: per-cluster seed nodes, cluster-scoped roles + singletons; rig models the real topology | No |
+| 6 | Mesh partition: per-cluster seed nodes, cluster-scoped roles + singletons; rig models the real topology | No — **DONE 2026-07-24**, see `2026-07-22-per-cluster-mesh-program.md` §Phase 6 and `2026-07-24-mesh-phase6-partition-and-colocation.md` |
 | 7 | Failover drill (both directions, per §6.2); live gate | No |
 
 Phases 3 and 4 are the ones that change a running system's data path rather than its wiring, and each