feat(audit): M5.3 response-capture increments — request headers, ceiling-hits counter, per-method body opt-out (T7)

1. Request headers in Extra JSON (AuditWriteMiddleware): adds a `requestHeaders`
   object to the existing Extra JSON alongside remoteIp/userAgent; headers whose
   names appear in AuditLogOptions.HeaderRedactList (Authorization, X-Api-Key,
   Cookie, Set-Cookie by default) are replaced with "<redacted>" using
   OrdinalIgnoreCase matching — same policy as ScadaBridgeAuditRedactor.

2. AuditInboundCeilingHits counter: new IAuditInboundCeilingHitsCounter interface
   + NoOpAuditInboundCeilingHitsCounter default; AuditCentralHealthSnapshot
   implements the interface (Interlocked field, thread-safe) and exposes
   AuditInboundCeilingHits on IAuditCentralHealthSnapshot; AddAuditLog registers
   the NoOp default, AddAuditLogCentralMaintenance forwards to the snapshot;
   AuditWriteMiddleware accepts the counter as an optional ctor arg and increments
   it once per request where either the request or response body hit the cap.

3. Per-method SkipBodyCapture opt-out: adds SkipBodyCapture bool to
   PerTargetRedactionOverride; AuditWriteMiddleware consults the per-target
   override map at the start of InvokeAsync (before EnableBuffering) and, when
   set, skips body read + capture entirely — the audit row still emits with
   headers/metadata but null RequestSummary/ResponseSummary; truncation flags
   are also cleared so the ceiling-hits counter is not bumped for opted-out methods.

src/ZB.MOM.WW.ScadaBridge.AuditLog/Central/NoOpAuditInboundCeilingHitsCounter.cs

@@ -0,0 +1,13 @@
+namespace ZB.MOM.WW.ScadaBridge.AuditLog.Central;
+
+/// <summary>
+/// Default <see cref="IAuditInboundCeilingHitsCounter"/> binding used when
+/// the central health snapshot is not wired (e.g. site composition roots,
+/// test harnesses that have no health dashboard). All increments are silently
+/// dropped — correct for environments that have no audit KPI surface.
+/// </summary>
+public sealed class NoOpAuditInboundCeilingHitsCounter : IAuditInboundCeilingHitsCounter
+{
+    /// <inheritdoc/>
+    public void Increment() { }
+}