feat(health): AuditRedactionFailure counter + bridge (#23 M5)

Bundle C task M5-T7 — surface DefaultAuditPayloadFilter redactor
over-redactions as a Site Health metric so a misconfigured /
catastrophic regex shows up on /monitoring/health rather than
disappearing into a NoOp sink.

  - SiteHealthReport: new 'AuditRedactionFailure' int field
    (defaulted to 0 for back-compat with existing producers/tests).
  - ISiteHealthCollector / SiteHealthCollector:
    new IncrementAuditRedactionFailure() — per-interval atomic
    counter with Interlocked, reset on CollectReport, mirroring
    the M2 Bundle G SiteAuditWriteFailures pattern.
  - HealthMetricsAuditRedactionFailureCounter: new bridge in
    ScadaLink.AuditLog.Site that forwards IAuditRedactionFailureCounter
    increments to ISiteHealthCollector — mirrors
    HealthMetricsAuditWriteFailureCounter one-for-one.
  - AddAuditLogHealthMetricsBridge: now ALSO Replaces the
    NoOpAuditRedactionFailureCounter binding with the health-metrics
    bridge, so a single AddAuditLogHealthMetricsBridge() call wires
    both the M2 Bundle G write-failure counter and the M5 Bundle C
    redaction-failure counter into the health report.

Site-side only for M5 — the filter also runs on CentralAuditWriter
and AuditLogIngestActor (where it just keeps the NoOp default), but
a central-side health-metric surface for AuditRedactionFailure is
deferred to M6 alongside the rest of the central health collector
work.

Tests:
  - AuditRedactionFailureMetricTests (HealthMonitoring) covers the
    SiteHealthCollector increment/report/reset shape (3 tests).
  - HealthMetricsAuditRedactionFailureCounterTests (AuditLog) covers
    the AuditLog → HealthMonitoring bridge (3 tests).
  - Existing CountCapturingHealthCollector stub in
    DeploymentManagerRedeployTests extended with the new no-op
    interface method.

Verified: dotnet build clean, all 24 test projects green
(the only Failed at first ScadaLink.SiteRuntime.Tests run was the
known-flaky InstanceActorChildAttributeRaceTests; passes on re-run
in isolation and full suite, unrelated to these changes).

tests/ScadaLink.AuditLog.Tests/Site/HealthMetricsAuditRedactionFailureCounterTests.cs

@@ -0,0 +1,49 @@
+using NSubstitute;
+using ScadaLink.AuditLog.Site;
+using ScadaLink.HealthMonitoring;
+
+namespace ScadaLink.AuditLog.Tests.Site;
+
+/// <summary>
+/// Bundle C (M5-T7) — the <see cref="HealthMetricsAuditRedactionFailureCounter"/>
+/// adapter is the production binding for
+/// <see cref="ScadaLink.AuditLog.Payload.IAuditRedactionFailureCounter"/> on
+/// site nodes; it forwards every <see cref="DefaultAuditPayloadFilter"/>
+/// redactor over-redaction event into the shared
+/// <see cref="ISiteHealthCollector"/> so the site health report surfaces the
+/// count as <c>AuditRedactionFailure</c>. Mirrors the M2 Bundle G
+/// HealthMetricsAuditWriteFailureCounter shape one-for-one.
+/// </summary>
+public class HealthMetricsAuditRedactionFailureCounterTests
+{
+    [Fact]
+    public void Increment_Routes_To_Collector_IncrementAuditRedactionFailure()
+    {
+        var collector = Substitute.For<ISiteHealthCollector>();
+        var counter = new HealthMetricsAuditRedactionFailureCounter(collector);
+
+        counter.Increment();
+
+        collector.Received(1).IncrementAuditRedactionFailure();
+    }
+
+    [Fact]
+    public void Increment_Multiple_Calls_Route_To_Collector_Each_Time()
+    {
+        var collector = Substitute.For<ISiteHealthCollector>();
+        var counter = new HealthMetricsAuditRedactionFailureCounter(collector);
+
+        counter.Increment();
+        counter.Increment();
+        counter.Increment();
+
+        collector.Received(3).IncrementAuditRedactionFailure();
+    }
+
+    [Fact]
+    public void Construction_With_Null_Collector_Throws_ArgumentNullException()
+    {
+        Assert.Throws<ArgumentNullException>(
+            () => new HealthMetricsAuditRedactionFailureCounter(null!));
+    }
+}