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

src/NATS.Server/Monitoring/MonitorServer.cs

@@ -34,7 +34,7 @@ public sealed class MonitorServer : IAsyncDisposable
         _app = builder.Build();
         var basePath = options.MonitorBasePath ?? "";
 
-        _varzHandler = new VarzHandler(server, options);
+        _varzHandler = new VarzHandler(server, options, loggerFactory);
         _connzHandler = new ConnzHandler(server);
         _subszHandler = new SubszHandler(server);
         _jszHandler = new JszHandler(server, options);
@@ -59,7 +59,7 @@ public sealed class MonitorServer : IAsyncDisposable
         _app.MapGet(basePath + "/healthz", () =>
         {
             stats.HttpReqStats.AddOrUpdate("/healthz", 1, (_, v) => v + 1);
-            return Results.Ok("ok");
+            return Results.Ok(HealthStatus.Ok());
         });
         _app.MapGet(basePath + "/varz", async (HttpContext ctx) =>
         {