feat(localdb): replication health check + meter export

LocalDbReplicationHealthCheck reports Healthy when replication is default-OFF or
LocalDb is absent (admin-only graphs) - so a plain node is never degraded by it -
Degraded when configured-but-disconnected, connected-with-unknown-backlog (a failed
oplog poll must not read as zero), or connected-with-backlog past the threshold.
Never Unhealthy: a replication fault does not stop the node serving its address
space. Pure decision core is table-tested; registered unconditionally via a factory
so AddOtOpcUaHealth keeps its no-arg signature and resolves ISyncStatus optionally.

Adds LocalDbMetrics.MeterName to the observability allowlist. o.Meters is a strict
allowlist with no wildcard, so the localdb.sync.* / localdb.oplog.depth series were
otherwise silently absent from /metrics - the omission a ScadaBridge live gate
caught.

src/Server/ZB.MOM.WW.OtOpcUa.Host/Observability/ObservabilityExtensions.cs

@@ -1,4 +1,5 @@
 using Microsoft.Extensions.Configuration;
+using ZB.MOM.WW.LocalDb.Replication;
 using ZB.MOM.WW.OtOpcUa.Commons.Observability;
 using ZB.MOM.WW.Telemetry;
 
@@ -27,7 +28,11 @@ public static class ObservabilityExtensions
         return services.AddZbTelemetry(o =>
         {
             o.ServiceName = "otopcua";
-            o.Meters = [OtOpcUaTelemetry.MeterName];
+            // o.Meters is a STRICT allowlist — ZbTelemetry adds only the named meters, with no
+            // wildcard. The LocalDb replication engine publishes under its own meter name, so
+            // without this entry its localdb.sync.* / localdb.oplog.depth series are silently absent
+            // from /metrics on driver nodes (the exact omission a ScadaBridge live gate caught).
+            o.Meters = [OtOpcUaTelemetry.MeterName, LocalDbMetrics.MeterName];
             o.ActivitySources = [OtOpcUaTelemetry.ActivitySourceName];
             if (Enum.TryParse<ZbExporter>(configuration["OtOpcUa:Telemetry:Exporter"], ignoreCase: true, out var exporter))
                 o.Exporter = exporter;