refactor(fleet): #542 delete the dead fleet-status chain (broadcaster, SignalR bridge, hub, messages)

#542 filed FleetStatusBroadcaster as blind to site nodes since the Phase 6 per-cluster mesh
split: it derives "the fleet" from central's own Akka gossip ring, which after the split is
just central's own pair. Scoping the cross-mesh rewrite found the deeper truth — the whole
chain is dead end to end, so this deletes it rather than reviving it.

  - Zero consumers. FleetStatusBroadcaster published FleetStatusChanged on the DPS
    "fleet-status" topic; FleetStatusSignalRBridge forwarded it to FleetStatusHub
    ("/hubs/fleet-status"); nothing anywhere connected. The AdminUI bans self-connecting
    HubConnections, no browser JS subscribes, and /fleet (Fleet.razor) reads
    NodeDeploymentState from the ConfigDb plus IClusterRoleInfo on a 5 s poll instead.
  - Its second input never existed. DriverHostStatusHeartbeat had no production sender —
    only the broadcaster's own test told it — so CurrentRevision was always null and the
    30 s staleness -> Degraded flip could never fire.
  - Post-Phase-6 DPS is pair-local, so even the central-only view it did produce was an
    accident of topology rather than a design.

The fleet visibility that actually works is unchanged and already cross-mesh-correct:
/fleet over NodeDeploymentState, and the four Phase 5 per-node telemetry dials.

Precedent for deleting inert machinery rather than activating it: #522 (driver stability
tiers), #507 (discovered-node injection), #525 (GetMemoryFootprint).

Deleted: FleetStatusBroadcaster (+ its nested DriverHostStatusHeartbeat), its admin
singleton registration and FleetStatusBroadcasterKey, FleetStatusSignalRBridge and its
key, FleetStatusHub and its route mapping, and the FleetStatusChanged / FleetNodeStatus /
FleetNodeHealth messages. Both Fleet/ directories survive — ControlPlane keeps
ClusterNodeAddressReconciler, Commons keeps GetDiagnostics. Docs swept where they claimed
a fleet-status channel exists (Telemetry.md's Phase 5 non-migrated channels,
Configuration.md, CLAUDE.md); completed-program plan docs under docs/plans and docs/v2 are
left as the historical record they are.

Build 0 errors, 868 warnings — byte-identical to master's rebuild baseline.
ControlPlane.Tests 231/231, AdminUI.Tests 1109/1109.

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

src/Core/ZB.MOM.WW.OtOpcUa.Commons/Messages/Admin/StartDeploymentResult.cs

@@ -13,7 +13,7 @@ public enum StartDeploymentOutcome
 /// <summary>
 /// Reply from the <c>AdminOperationsActor</c> singleton. <c>Accepted</c> means the snapshot
 /// was sealed and a <c>Deployment</c> row was created; the in-flight deployment can be
-/// tracked through fleet-status broadcasts.
+/// tracked through the per-node <c>NodeDeploymentState</c> rows the AdminUI's /fleet page reads.
 /// </summary>
 public sealed record StartDeploymentResult(
     StartDeploymentOutcome Outcome,

src/Core/ZB.MOM.WW.OtOpcUa.Commons/Messages/Fleet/FleetStatusChanged.cs

@@ -1,21 +0,0 @@
-using ZB.MOM.WW.OtOpcUa.Commons.Types;
-
-namespace ZB.MOM.WW.OtOpcUa.Commons.Messages.Fleet;
-
-public enum FleetNodeHealth { Healthy, Degraded, Unreachable }
-
-public sealed record FleetNodeStatus(
-    NodeId NodeId,
-    FleetNodeHealth Health,
-    RevisionHash? CurrentRevision,
-    DateTime LastSeenUtc);
-
-/// <summary>
-/// Periodic fleet-wide status broadcast pushed by <c>FleetStatusBroadcaster</c> to admin UI
-/// subscribers via SignalR.
-/// </summary>
-public sealed record FleetStatusChanged(
-    IReadOnlyList<FleetNodeStatus> Nodes,
-    DeploymentId? CurrentDeployment,
-    DateTime AsOfUtc,
-    CorrelationId CorrelationId);