refactor(inbound-api): use the shared ZB.MOM.WW.Health IActiveNodeGate (ScadaBridge#80)

The InboundAPI carried its own IActiveNodeGate (implemented by Host/Health/ActiveNodeGate)
whose rule already matched the shared Health 0.3.0 AkkaActiveNodeGate — both route to
ClusterActiveNode (oldest Up member). The private interface and implementation are deleted;
InboundAPI references ZB.MOM.WW.Health (0.3.0, already pinned) and InboundApiEndpointFilter,
AuditWriteMiddleware, InboundMethodWarmupService and FlowDebugRunner consume
ZB.MOM.WW.Health.IActiveNodeGate. The Central branch of Program.cs registers
AkkaActiveNodeGate (unscoped, like the active-node health check).

Warm-up behaviour is kept: the shared gate answers false while no ActorSystem resolves, while
this member is not Up, and on any cluster-init fault. It resolves the ActorSystem through the
existing DI singleton bridge (GetOrCreateActorSystem), the same path the health probes use.

Tests: CompositionRoot asserts the shared gate type (fails with the registration removed);
the evaluator wiring test now drives AkkaActiveNodeGate; new warm-up test (no ActorSystem ->
not active). Nothing was missing from the Health 0.3.0 package.

(ScadaBridge#80)

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

src/ZB.MOM.WW.ScadaBridge.Host/Program.cs

@@ -603,15 +603,17 @@ try
             sp.GetRequiredService<IOptions<NodeOptions>>(),
             sp.GetRequiredService<ILogger<ClusterBootstrapCoordinator>>()));
 
-        // Register the production IActiveNodeGate implementation so
-        // standby-node gating is actually enforced (the InboundApiEndpointFilter
-        // consults IActiveNodeGate and defaults to "allow" when none is registered,
-        // which leaves the design's "central cluster only (active node)" guarantee
-        // unenforced in deployed binaries). The gate is backed by the same oldest-member
-        // evaluator (ClusterActivityEvaluator, which delegates to the shared ClusterActiveNode) as
-        // the active-node check above, so the inbound API and the /health/active endpoint Traefik
-        // routes against agree on which node is active.
-        builder.Services.AddSingleton<ZB.MOM.WW.ScadaBridge.InboundAPI.IActiveNodeGate, ActiveNodeGate>();
+        // Register the production active-node gate so standby-node gating is actually enforced
+        // (the InboundApiEndpointFilter consults IActiveNodeGate and defaults to "allow" when none
+        // is registered, which leaves the design's "central cluster only (active node)" guarantee
+        // unenforced in deployed binaries). Since Gitea #80 this is the SHARED seam
+        // (ZB.MOM.WW.Health.IActiveNodeGate) with the shared AkkaActiveNodeGate, unscoped like the
+        // active-node check above — both route to ClusterActiveNode, so the inbound API and the
+        // /health/active endpoint Traefik routes against can never disagree on which node is
+        // active. Warm-up stays safe: the gate resolves the ActorSystem through the singleton
+        // bridge above and answers false until this member is Up (and on any cluster-init fault).
+        builder.Services.AddSingleton<ZB.MOM.WW.Health.IActiveNodeGate>(
+            sp => new ZB.MOM.WW.Health.Akka.AkkaActiveNodeGate(sp));
 
         // Warm the inbound method compile cache in the BACKGROUND once the host is running and
         // this node is the active one (review 2026-10-21 05/U3). Registered after