feat: add atomic batch publish engine & versioning support (Tasks 9-10)

- AtomicBatchPublishEngine: stage/commit/rollback semantics for batch publish
- JsVersioning: API level negotiation and stream/consumer metadata
- Fix NormalizeConfig missing AllowAtomicPublish, Metadata, PersistMode copy
- 46 batch publish tests + 67 versioning tests, all passing

src/NATS.Server/JetStream/StreamManager.cs

@@ -63,6 +63,13 @@ public sealed class StreamManager
         if (normalized.SubjectDeleteMarkerTtlMs > 0 && !string.IsNullOrWhiteSpace(normalized.Mirror))
             return JetStreamApiResponse.ErrorResponse(10054, "mirror configuration can not have subject delete marker TTL");
 
+        // Go: NewJSMirrorWithAtomicPublishError (10198) — mirror + AllowAtomicPublish is invalid.
+        // Reference: server/stream.go:1735-1737
+        if (normalized.AllowAtomicPublish && !string.IsNullOrWhiteSpace(normalized.Mirror))
+            return JetStreamApiResponse.ErrorResponse(
+                AtomicBatchPublishErrorCodes.MirrorWithAtomicPublish,
+                "stream mirrors can not also use atomic publishing");
+
         // Go: RePublish cycle detection — destination must not overlap stream subjects.
         // Reference: server/stream.go:1060-1080 (checkRePublish)
         if (!string.IsNullOrWhiteSpace(normalized.RePublishDest))
@@ -389,6 +396,14 @@ public sealed class StreamManager
             SubjectDeleteMarkerTtlMs = config.SubjectDeleteMarkerTtlMs,
             // Go: StreamConfig.AllowMsgSchedules
             AllowMsgSchedules = config.AllowMsgSchedules,
+            // Go: StreamConfig.AllowMsgCounter — CRDT counter semantics
+            AllowMsgCounter = config.AllowMsgCounter,
+            // Go: StreamConfig.AllowAtomicPublish — atomic batch publish
+            AllowAtomicPublish = config.AllowAtomicPublish,
+            // Go: StreamConfig.PersistMode — async vs sync persistence
+            PersistMode = config.PersistMode,
+            // Go: StreamConfig.Metadata — user and server key/value metadata
+            Metadata = config.Metadata == null ? null : new Dictionary<string, string>(config.Metadata),
         };
 
         return copy;