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/GAPS.md

@@ -131,11 +131,3 @@ after `ZB.MOM.WW.Health` @ 0.1.0 is published. The library build itself (nupkgs,
 separate task. This is consistent with how `ZB.MOM.WW.Auth` and `ZB.MOM.WW.Theme` are structured:
 the library is built first; adoption by the three apps is the next step.
 
-## Decisions still open
-
-- Whether `GrpcDependencyHealthCheck` takes a named channel (from DI) or a raw `ChannelBase` —
-  affects how MxAccessGateway registers the worker-IPC probe without a standard gRPC channel.
-- Whether `IActiveNodeGate` lives in `ZB.MOM.WW.Health` (making it a hard dependency) or stays
-  in ScadaBridge's `InboundAPI` project (keeping the gate as a ScadaBridge concern).
-- Whether the `OtOpcUaCompat` preset for `AkkaClusterHealthCheck` is a named constant or just
-  documented configuration.