fix(site-secrets): report every site node's secret mirror failures on the health report (M1)

A DeployedSecretsMirror failure on the STANDBY node (e.g. a master-key mismatch
that stops a deployed secret decrypting there) was only logged on that node:
site health reports are sent by the active node only, so central never saw it.

- New 12th LocalDb-replicated table secret_mirror_status (node_name PK,
  failures_json of {SecretName, Message}, checked_at; no FKs). Each node's
  mirror writes only its own row, and only when its failure set changes plus
  once per start-up (every write replicates via CDC). Best-effort: a failed
  write is a Warning and is retried next pass. Node key = INodeIdentityProvider
  NodeName, falling back to the machine name.
- SecretMirrorStatusReporter (SiteRuntime, every node, 30 s) reads every row
  into ISiteHealthCollector.SetSecretMirrorStatuses -> additive nullable
  SiteHealthReport.SecretMirrorStatuses (null = no data).
- Wire: SiteHealthReportDto.secret_mirror_statuses = 33 (presence wrapper so
  null != empty); vendored CentralControl.cs regenerated; mapper both ways.
- Central UI Health card: 'Secret mirror failing' badge + compact per-node
  node / secret / message list.
- Tests: mirror status write-on-change/first-pass/failure isolation, storage
  round-trip, reporter/collector, DTO mapper round-trip incl. null/empty,
  bUnit, replicated-table set (twelve) + FK guard wording.

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Secrets/DeployedSecretsMirror.cs

@@ -1,7 +1,9 @@
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Artifacts;
+using ZB.MOM.WW.ScadaBridge.Commons.Messages.Health;
 using ZB.MOM.WW.ScadaBridge.SiteRuntime.Persistence;
 using ZB.MOM.WW.Secrets.Abstractions;
 
@@ -153,6 +155,18 @@ public sealed record MirrorResult(
 /// so a LATER failure — even one with an identical fingerprint — logs at Error again. This state
 /// is in-memory only (per node process), which matches the ledger's own node-local scope.
 /// </para>
+/// <para>
+/// <b>Status row for central (review finding M1).</b> A failure on the STANDBY node used to be
+/// visible only in that node's own log — site health reports are sent by the active node only.
+/// After each pass this mirror records its node's current failure set (secret name + message,
+/// never a value) in the LocalDb-replicated <c>secret_mirror_status</c> table, keyed by node
+/// name; <c>SecretMirrorStatusReporter</c> on the active node reads every node's row onto the
+/// health report. Because every write replicates via CDC, the row is written only when the
+/// failure set (compared as sorted name+message pairs) differs from what this process last
+/// wrote — plus once on the first pass after start-up, so a restart refreshes a stale row. The
+/// write is best-effort: a failure logs a Warning (repeats at Debug) and is retried on the next
+/// pass, and never affects the pass's own <see cref="MirrorResult"/>.
+/// </para>
 /// </remarks>
 public sealed class DeployedSecretsMirror : BackgroundService
 {
@@ -165,6 +179,17 @@ public sealed class DeployedSecretsMirror : BackgroundService
     private readonly IOptions<SiteRuntimeOptions> _options;
     private readonly ILogger<DeployedSecretsMirror> _logger;
     private readonly TimeProvider _time;
+    private readonly string _nodeName;
+
+    /// <summary>
+    /// The failure set (sorted name+message pairs) this process last wrote successfully to
+    /// <c>secret_mirror_status</c>, or <see langword="null"/> before the first successful write
+    /// — which is what forces the once-per-start-up write (review finding M1).
+    /// </summary>
+    private IReadOnlyList<SecretMirrorFailure>? _lastWrittenStatus;
+
+    /// <summary>Whether a failed status write has already been logged at Warning (de-spam).</summary>
+    private bool _statusWriteFailureLogged;
 
     private readonly SemaphoreSlim _gate = new(1, 1);
     private bool _disposed;
@@ -199,6 +224,11 @@ public sealed class DeployedSecretsMirror : BackgroundService
     /// <param name="options">Supplies <see cref="SiteRuntimeOptions.DeployedSecretsMirrorInterval"/>.</param>
     /// <param name="logger">Logger instance. Never logs secret values — names, revisions, and KEK ids only.</param>
     /// <param name="time">Clock driving the reconcile loop's <see cref="PeriodicTimer"/> and the tombstone-recovery stamp.</param>
+    /// <param name="nodeIdentity">
+    /// Supplies this node's name (<c>node-a</c>/<c>node-b</c>), the key of its
+    /// <c>secret_mirror_status</c> row. Optional: when absent or unconfigured, the machine name
+    /// is used instead.
+    /// </param>
     public DeployedSecretsMirror(
         SiteStorageService storage,
         ISecretStore store,
@@ -206,7 +236,8 @@ public sealed class DeployedSecretsMirror : BackgroundService
         ISecretCacheInvalidator? invalidator,
         IOptions<SiteRuntimeOptions> options,
         ILogger<DeployedSecretsMirror> logger,
-        TimeProvider time)
+        TimeProvider time,
+        INodeIdentityProvider? nodeIdentity = null)
     {
         _storage = storage ?? throw new ArgumentNullException(nameof(storage));
         _store = store ?? throw new ArgumentNullException(nameof(store));
@@ -215,6 +246,7 @@ public sealed class DeployedSecretsMirror : BackgroundService
         _options = options ?? throw new ArgumentNullException(nameof(options));
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
         _time = time ?? throw new ArgumentNullException(nameof(time));
+        _nodeName = nodeIdentity?.NodeName ?? Environment.MachineName;
     }
 
     /// <summary>
@@ -314,6 +346,8 @@ public sealed class DeployedSecretsMirror : BackgroundService
                     rows.Count(r => !r.IsRemoved) + unreadable.Count(u => !u.IsRemoved), failed.Count);
             }
 
+            await RecordStatusIfChangedAsync(failedNames, failed).ConfigureAwait(false);
+
             return result;
         }
         finally
@@ -322,6 +356,42 @@ public sealed class DeployedSecretsMirror : BackgroundService
         }
     }
 
+    /// <summary>
+    /// Writes this node's <c>secret_mirror_status</c> row when the pass's failure set differs
+    /// from the last one this process wrote (or nothing has been written yet since start-up).
+    /// Best-effort: never throws, so the pass result is unaffected by a status-write fault.
+    /// See the class remarks (review finding M1).
+    /// </summary>
+    private async Task RecordStatusIfChangedAsync(IReadOnlyList<string> failedNames, IReadOnlyList<string> failed)
+    {
+        var current = failedNames
+            .Select((name, i) => new SecretMirrorFailure(name, failed[i]))
+            .OrderBy(f => f.SecretName, StringComparer.Ordinal)
+            .ThenBy(f => f.Message, StringComparer.Ordinal)
+            .ToList();
+
+        if (_lastWrittenStatus is not null && _lastWrittenStatus.SequenceEqual(current))
+        {
+            return;
+        }
+
+        try
+        {
+            await _storage.SetSecretMirrorStatusAsync(_nodeName, current, _time.GetUtcNow()).ConfigureAwait(false);
+            _lastWrittenStatus = current;
+            _statusWriteFailureLogged = false;
+        }
+        catch (Exception ex)
+        {
+            _logger.Log(
+                _statusWriteFailureLogged ? LogLevel.Debug : LogLevel.Warning,
+                ex,
+                "Failed to record the deployed secrets mirror status for node {NodeName}; retrying next pass",
+                _nodeName);
+            _statusWriteFailureLogged = true;
+        }
+    }
+
     /// <summary>
     /// Handles a tombstoned <c>deployed_secrets</c> row: deletes it from this node's store, but
     /// only if this node had previously ledgered it as mirrored — an out-of-band, same-named