Fix all baseline code-review findings across the six shared libraries

Resolves the 35 findings from the 2026-06-01 baseline (commit 26ba1c7),
test-first for every behavioral change. +51 tests (331 -> 382 passing, 0 failed).

- Telemetry-001 (HIGH): RedactionEnricher now honours property removal, so a
  redactor that drops a key actually scrubs the secret from the event.
- Auth: LDAP validator ValidateOnStart; API-key verify no longer fails on a
  best-effort MarkUsed write or a corrupt scopes column (fail-closed); LDAP cert
  validation hook; KeyPrefix persistence aligned; README algorithm corrected.
- Health: Akka checks return Degraded (not throw) when the cluster isn't up yet;
  GrpcDependencyHealthCheck catch-all; null 'description' rendered; composite
  endpoint builder; XML docs shipped.
- Audit: CompositeAuditWriter no longer re-throws OperationCanceledException;
  TruncatingAuditRedactor over-redact scrubs Target + safe negative max; options
  record; XML docs shipped.
- Configuration: TryAddEnumerable idempotent registration; consistent port
  quoting; strict invariant port parsing; XML docs + README packaged.
- Theme: mobile toggle is now CSS-only (no Bootstrap JS); token/CSS hygiene;
  XML docs on the public parameter surface.

Shared-contract/spec docs updated where the code was the source of truth
(observability service.instance.id, MapZbMetrics, redactor reach). All changes
additive/back-compatible at v0.1.0. code-reviews bookkeeping follows separately.

ZB.MOM.WW.Health/tests/ZB.MOM.WW.Health.Tests/ResponseWriterTests.cs

@@ -31,7 +31,7 @@ public sealed class ResponseWriterTests
     }
 
     private static async Task<HttpResponseMessage> GetReadyAsync(
-        HealthStatus status, string description = "db reachable")
+        HealthStatus status, string? description = "db reachable")
     {
         var builder = WebApplication.CreateBuilder();
         builder.WebHost.UseTestServer();
@@ -66,6 +66,24 @@ public sealed class ResponseWriterTests
         Assert.Equal("db reachable", db.GetProperty("description").GetString());
     }
 
+    [Fact]
+    public async Task ReadyEndpoint_NullDescription_EmitsDescriptionKeyAsNull()
+    {
+        // A check that produces no description must still emit the "description" key with a JSON null
+        // value (matching the spec §3 example and the HealthChecks.UI.Client shape) rather than
+        // dropping the key — so consumers can read entries.<name>.description without handling a
+        // missing property.
+        var response = await GetReadyAsync(HealthStatus.Healthy, description: null);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        using var doc = JsonDocument.Parse(await response.Content.ReadAsStringAsync());
+        var db = doc.RootElement.GetProperty("entries").GetProperty("db");
+
+        Assert.True(db.TryGetProperty("description", out var description), "description key must be present");
+        Assert.Equal(JsonValueKind.Null, description.ValueKind);
+    }
+
     [Fact]
     public async Task ReadyEndpoint_Degraded_Returns200_WithDegradedStatus()
     {