Fix E2E test gaps and add comprehensive E2E + parity test suites

- Fix pull consumer fetch: send original stream subject in HMSG (not inbox)
  so NATS client distinguishes data messages from control messages
- Fix MaxAge expiry: add background timer in StreamManager for periodic pruning
- Fix JetStream wire format: Go-compatible anonymous objects with string enums,
  proper offset-based pagination for stream/consumer list APIs
- Add 42 E2E black-box tests (core messaging, auth, TLS, accounts, JetStream)
- Add ~1000 parity tests across all subsystems (gaps closure)
- Update gap inventory docs to reflect implementation status

tests/NATS.Server.Tests/TlsHelperTests.cs

@@ -35,6 +35,45 @@ public class TlsHelperTests
         finally { File.Delete(certPath); File.Delete(keyPath); }
     }
 
+    [Fact]
+    public void LoadCaCertificates_rejects_non_certificate_pem_block()
+    {
+        var (_, key) = GenerateTestCert();
+        var pemPath = Path.GetTempFileName();
+        try
+        {
+            File.WriteAllText(pemPath, key.ExportPkcs8PrivateKeyPem());
+            Should.Throw<InvalidDataException>(() => TlsHelper.LoadCaCertificates(pemPath));
+        }
+        finally
+        {
+            File.Delete(pemPath);
+            key.Dispose();
+        }
+    }
+
+    [Fact]
+    public void LoadCaCertificates_loads_multiple_certificate_blocks()
+    {
+        var (certA, keyA) = GenerateTestCert();
+        var (certB, keyB) = GenerateTestCert();
+        var pemPath = Path.GetTempFileName();
+        try
+        {
+            File.WriteAllText(pemPath, certA.ExportCertificatePem() + certB.ExportCertificatePem());
+            var collection = TlsHelper.LoadCaCertificates(pemPath);
+            collection.Count.ShouldBe(2);
+        }
+        finally
+        {
+            File.Delete(pemPath);
+            certA.Dispose();
+            certB.Dispose();
+            keyA.Dispose();
+            keyB.Dispose();
+        }
+    }
+
     [Fact]
     public void MatchesPinnedCert_matches_correct_hash()
     {