docs(health): resolve spec/contract/gaps consistency (review fixes)

Applies canonical resolutions for eight settled decisions:
- GAPS: remove three stale "Decisions still open" bullets (#1 IActiveNodeGate placement, #2 GrpcChannel type, #3 OtOpcUaCompat named constant)
- Shared contract: AkkaClusterHealthCheck, ActiveNodeHealthCheck constructors take IServiceProvider (lazy ActorSystem, Degraded-when-not-ready)
- Shared contract: AkkaActiveNodeGate takes IServiceProvider; reads SelfMember+leader directly, null-guarded; does not proxy ActiveNodeHealthCheck
- Shared contract: DatabaseHealthCheckOptions.Probe renamed to ProbeQuery; consumer matrix updated
- Shared contract: settled AddZbHealthChecks open question removed (spec §5 is per-project AddHealthChecks)
- SPEC §2.2: OtOpcUaCompat Leaving/Exiting cell updated from — to Degraded + footnote; §2.3 startup-safety note added
- README: status line corrected from "built and tested" to "scaffolded … implementation is follow-on (task #7)"; IActiveNodeGate "left per-project" bullet removed
- OtOpcUa current-state: AddZbHealthChecks → AddHealthChecks().AddCheck<...>(); IClusterRoleInfo note reframed as accepted trade-off
- ScadaBridge current-state: IActiveNodeGate bullet rewritten — interface moves to ZB.MOM.WW.Health on adoption, InboundApiEndpointFilter references shared interface

components/health/README.md

@@ -65,8 +65,6 @@ code-verified detail and its adoption plan.
   keep as a bespoke `/info` endpoint.
 - The x86 worker process — out of process and out of scope; the gateway-side
   `GrpcDependencyHealthCheck` observes it indirectly.
-- Per-project `IActiveNodeGate` contract location (whether the interface lives in the shared
-  library or in each project's own surface).
 
 ## Package structure
 
@@ -84,6 +82,6 @@ all three.
 ## Component status
 
 **Status: Draft.** Spec and shared-contract written; current-state docs verified; GAPS backlog
-populated. Library (`ZB.MOM.WW.Health` @ 0.1.0) built and tested in this repo at
-[`../../ZB.MOM.WW.Health/`](../../ZB.MOM.WW.Health/). Adoption by the three apps is a follow-on
-tracked in [`GAPS.md`](GAPS.md).
+populated. Library scaffolded at [`../../ZB.MOM.WW.Health/`](../../ZB.MOM.WW.Health/); source
+implementation is a follow-on (task #7 in the adoption backlog). Adoption by the three apps is
+a further follow-on tracked in [`GAPS.md`](GAPS.md).