feat(secrets): 0.6.3 — hub sweep outcome logging (in-sync debug + hourly heartbeat + recovered) and ISecretsHubSyncStatus

GrpcSecretSyncService's background sweep now records outcomes on a new
SecretsHubSyncStatus (registered singleton, exposed as public
ISecretsHubSyncStatus) and logs three new events on the outcome-recording
path: EventId 4 (Debug, every in-sync sweep), EventId 5 (Information, the
same outcome throttled to at most once per the new
SecretsGrpcHubClientOptions.InSyncLogInterval, default 1h), and EventId 6
(Information, the first sweep to succeed after one or more failures).
EventIds 1-3 are unchanged; the raw internal SweepAsync still throws on
failure exactly as before. Not yet published to the Gitea feed and
ScadaBridge is not re-pinned — that is a separate, later step.

ZB.MOM.WW.Secrets/src/ZB.MOM.WW.Secrets.Replicator.Grpc/SecretsGrpcHubClientOptions.cs

@@ -77,6 +77,20 @@ public sealed class SecretsGrpcHubClientOptions
     /// </summary>
     public TimeSpan CallDeadline { get; set; } = TimeSpan.FromSeconds(30);
 
+    /// <summary>
+    /// How often an in-sync sweep (nothing to pull) is allowed to log an Information-level
+    /// heartbeat. Defaults to one hour. Must be positive.
+    /// </summary>
+    /// <remarks>
+    /// A converged follower sweeps every <see cref="SyncInterval"/> — 30 seconds by default — and
+    /// finds nothing new almost every time. Logging that outcome at Information on every sweep
+    /// would drown the log; staying silent forever would make "the sweep loop is alive and the hub
+    /// still agrees with this node" unobservable between the rare sweeps that actually pull
+    /// something. Every sweep still logs at Debug regardless of this interval, so a verbose log
+    /// level shows the true cadence when it is needed.
+    /// </remarks>
+    public TimeSpan InSyncLogInterval { get; set; } = TimeSpan.FromHours(1);
+
     /// <summary>
     /// Throws if the options are unusable. Called by the DI extension at registration time so a
     /// misconfigured node fails at startup rather than on the first silent sweep failure.
@@ -161,6 +175,13 @@ public sealed class SecretsGrpcHubClientOptions
                 $"gRPC secrets hub client CallDeadline must be positive " +
                 $"({sectionPath}:CallDeadline, was {CallDeadline}).");
         }
+
+        if (InSyncLogInterval <= TimeSpan.Zero)
+        {
+            throw new InvalidOperationException(
+                $"gRPC secrets hub client InSyncLogInterval must be positive " +
+                $"({sectionPath}:InSyncLogInterval, was {InSyncLogInterval}).");
+        }
     }
 
     /// <summary>The configuration section these options are bound from unless a caller overrides it.</summary>