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/Events/EventServerInfoCapabilityParityBatch1Tests.cs

@@ -0,0 +1,46 @@
+using System.Text.Json;
+using NATS.Server.Events;
+
+namespace NATS.Server.Tests.Events;
+
+public class EventServerInfoCapabilityParityBatch1Tests
+{
+    [Fact]
+    public void ServerCapability_flags_match_expected_values()
+    {
+        ((ulong)ServerCapability.JetStreamEnabled).ShouldBe(1UL << 0);
+        ((ulong)ServerCapability.BinaryStreamSnapshot).ShouldBe(1UL << 1);
+        ((ulong)ServerCapability.AccountNRG).ShouldBe(1UL << 2);
+    }
+
+    [Fact]
+    public void EventServerInfo_capability_methods_set_and_read_flags()
+    {
+        var info = new EventServerInfo();
+
+        info.SetJetStreamEnabled();
+        info.SetBinaryStreamSnapshot();
+        info.SetAccountNRG();
+
+        info.JetStream.ShouldBeTrue();
+        info.JetStreamEnabled().ShouldBeTrue();
+        info.BinaryStreamSnapshot().ShouldBeTrue();
+        info.AccountNRG().ShouldBeTrue();
+    }
+
+    [Fact]
+    public void ServerID_serializes_with_name_host_id_fields()
+    {
+        var payload = new ServerID
+        {
+            Name = "srv-a",
+            Host = "127.0.0.1",
+            Id = "N1",
+        };
+
+        var json = JsonSerializer.Serialize(payload);
+        json.ShouldContain("\"name\":\"srv-a\"");
+        json.ShouldContain("\"host\":\"127.0.0.1\"");
+        json.ShouldContain("\"id\":\"N1\"");
+    }
+}