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/JetStream/Models/StreamConfig.cs

@@ -8,7 +8,18 @@ public sealed class StreamConfig
     public int MaxMsgs { get; set; }
     public long MaxBytes { get; set; }
     public int MaxMsgsPer { get; set; }
+    [System.Text.Json.Serialization.JsonIgnore]
     public int MaxAgeMs { get; set; }
+
+    /// <summary>
+    /// MaxAge in nanoseconds for JSON wire compatibility with Go server.
+    /// Go reference: StreamConfig.MaxAge is a time.Duration (nanoseconds in JSON).
+    /// </summary>
+    public long MaxAge
+    {
+        get => (long)MaxAgeMs * 1_000_000L;
+        set => MaxAgeMs = (int)(value / 1_000_000);
+    }
     public int MaxMsgSize { get; set; }
     public int MaxConsumers { get; set; }
     public int DuplicateWindowMs { get; set; }