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/EventCompressionTests.cs

@@ -168,4 +168,31 @@ public class EventCompressionTests : IDisposable
         EventCompressor.TotalUncompressed.ShouldBe(0L);
         EventCompressor.BytesSaved.ShouldBe(0L);
     }
+
+    [Fact]
+    public void GetAcceptEncoding_ParsesSnappyAndGzip()
+    {
+        EventCompressor.GetAcceptEncoding("gzip, snappy").ShouldBe(EventCompressionType.Snappy);
+        EventCompressor.GetAcceptEncoding("gzip").ShouldBe(EventCompressionType.Gzip);
+        EventCompressor.GetAcceptEncoding("br").ShouldBe(EventCompressionType.Unsupported);
+        EventCompressor.GetAcceptEncoding(null).ShouldBe(EventCompressionType.None);
+    }
+
+    [Fact]
+    public void CompressionHeaderConstants_MatchGo()
+    {
+        EventCompressor.AcceptEncodingHeader.ShouldBe("Accept-Encoding");
+        EventCompressor.ContentEncodingHeader.ShouldBe("Content-Encoding");
+    }
+
+    [Fact]
+    public void CompressAndDecompress_Gzip_RoundTrip_MatchesOriginal()
+    {
+        var payload = Encoding.UTF8.GetBytes("""{"server":"s1","data":"gzip-payload"}""");
+
+        var compressed = EventCompressor.Compress(payload, EventCompressionType.Gzip);
+        var restored = EventCompressor.Decompress(compressed, EventCompressionType.Gzip);
+
+        restored.ShouldBe(payload);
+    }
 }