feat(auditlog): HTTP header redaction stage (#23 M5)

src/ScadaLink.AuditLog/ServiceCollectionExtensions.cs

@@ -69,6 +69,12 @@ public static class ServiceCollectionExtensions
         // dependency picks up M5-T8 hot reloads on its own.
         services.AddSingleton<IAuditPayloadFilter, DefaultAuditPayloadFilter>();
 
+        // M5 Bundle B: per-stage redactor-failure counter. NoOp default;
+        // Bundle C replaces this binding with the Site Health Monitoring
+        // bridge that surfaces failures as AuditRedactionFailure on the site
+        // health report.
+        services.TryAddSingleton<IAuditRedactionFailureCounter, NoOpAuditRedactionFailureCounter>();
+
         // M2 Bundle E: site writer + telemetry options bindings.
         // BindConfiguration is not used because the configuration root supplied
         // by the caller may not be the application root — we go through the