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/LeafNodes/LeafSubKeyParityBatch2Tests.cs

@@ -0,0 +1,42 @@
+using NATS.Server.LeafNodes;
+using NATS.Server.Subscriptions;
+
+namespace NATS.Server.Tests.LeafNodes;
+
+public class LeafSubKeyParityBatch2Tests
+{
+    [Fact]
+    public void Constants_match_go_leaf_key_and_delay_values()
+    {
+        LeafSubKey.KeyRoutedSub.ShouldBe("R");
+        LeafSubKey.KeyRoutedSubByte.ShouldBe((byte)'R');
+        LeafSubKey.KeyRoutedLeafSub.ShouldBe("L");
+        LeafSubKey.KeyRoutedLeafSubByte.ShouldBe((byte)'L');
+        LeafSubKey.SharedSysAccDelay.ShouldBe(TimeSpan.FromMilliseconds(250));
+        LeafSubKey.ConnectProcessTimeout.ShouldBe(TimeSpan.FromSeconds(2));
+    }
+
+    [Fact]
+    public void KeyFromSub_matches_go_subject_and_queue_shape()
+    {
+        LeafSubKey.KeyFromSub(NewSub("foo")).ShouldBe("foo");
+        LeafSubKey.KeyFromSub(NewSub("foo", "bar")).ShouldBe("foo bar");
+    }
+
+    [Fact]
+    public void KeyFromSubWithOrigin_matches_go_routed_and_leaf_routed_shapes()
+    {
+        LeafSubKey.KeyFromSubWithOrigin(NewSub("foo")).ShouldBe("R foo");
+        LeafSubKey.KeyFromSubWithOrigin(NewSub("foo", "bar")).ShouldBe("R foo bar");
+        LeafSubKey.KeyFromSubWithOrigin(NewSub("foo"), "leaf").ShouldBe("L foo leaf");
+        LeafSubKey.KeyFromSubWithOrigin(NewSub("foo", "bar"), "leaf").ShouldBe("L foo bar leaf");
+    }
+
+    private static Subscription NewSub(string subject, string? queue = null)
+        => new()
+        {
+            Subject = subject,
+            Queue = queue,
+            Sid = Guid.NewGuid().ToString("N"),
+        };
+}