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

tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Hubs/TelemetryModeWiringTests.cs

@@ -16,12 +16,11 @@ namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests.Hubs;
 ///     Verifies the Phase 5 dark switch in <see cref="HubServiceCollectionExtensions.WithOtOpcUaSignalRBridges"/>:
 ///     <c>TelemetryDial:Mode = Dps</c> (default) spawns the four telemetry DPS bridge actors and NOT the
 ///     gRPC dial supervisor; <c>Grpc</c> spawns the dial supervisor and NONE of the four telemetry
-///     bridges. The fleet-status bridge (deferred / out of Phase 5 scope) is spawned in BOTH modes.
-///     The gate is proven on a real <see cref="ActorRegistry"/> from a started Akka host.
+///     bridges. The gate is proven on a real <see cref="ActorRegistry"/> from a started Akka host.
 /// </summary>
 public sealed class TelemetryModeWiringTests
 {
-    /// <summary>Dps mode: the four telemetry bridges + fleet bridge are registered; the dial supervisor is not.</summary>
+    /// <summary>Dps mode: the four telemetry bridges are registered; the dial supervisor is not.</summary>
     [Fact]
     public async Task Dps_mode_spawns_the_four_telemetry_bridges_and_not_the_dial_supervisor()
     {
@@ -31,7 +30,6 @@ public sealed class TelemetryModeWiringTests
         {
             var registry = host.Services.GetRequiredService<ActorRegistry>();
 
-            registry.TryGet<FleetStatusSignalRBridgeKey>(out _).ShouldBeTrue();
             registry.TryGet<AlertSignalRBridgeKey>(out _).ShouldBeTrue();
             registry.TryGet<ScriptLogSignalRBridgeKey>(out _).ShouldBeTrue();
             registry.TryGet<DriverStatusSignalRBridgeKey>(out _).ShouldBeTrue();
@@ -45,7 +43,7 @@ public sealed class TelemetryModeWiringTests
         }
     }
 
-    /// <summary>Grpc mode: the dial supervisor + fleet bridge are registered; none of the four telemetry bridges are.</summary>
+    /// <summary>Grpc mode: the dial supervisor is registered; none of the four telemetry bridges are.</summary>
     [Fact]
     public async Task Grpc_mode_spawns_the_dial_supervisor_and_none_of_the_four_telemetry_bridges()
     {
@@ -55,7 +53,6 @@ public sealed class TelemetryModeWiringTests
         {
             var registry = host.Services.GetRequiredService<ActorRegistry>();
 
-            registry.TryGet<FleetStatusSignalRBridgeKey>(out _).ShouldBeTrue();
             registry.TryGet<TelemetryDialSupervisorKey>(out _).ShouldBeTrue();
 
             registry.TryGet<AlertSignalRBridgeKey>(out _).ShouldBeFalse();