fix: resolve 19 JetStream test failures across 5 root causes

- HandleList: populate StreamNames/ConsumerNames alongside info lists
- ValidateConfigUpdate: allow clearing mirror/sources, accept even replicas
- ToWireFormat: add AccountInfo branch for $JS.API.INFO responses
- UpdateStream fixture: preserve existing retention policy on update
- Integration test: fix assertion to match valid account info response

src/NATS.Server/JetStream/Api/Handlers/ConsumerApiHandlers.cs

@@ -82,6 +82,7 @@ public static class ConsumerApiHandlers
         return new JetStreamApiResponse
         {
             ConsumerInfoList = page,
+            ConsumerNames = page.Select(c => c.Name ?? string.Empty).ToList(),
             PaginationTotal = all.Count,
             PaginationOffset = offset,
         };

src/NATS.Server/JetStream/Api/Handlers/StreamApiHandlers.cs

@@ -123,6 +123,7 @@ public static class StreamApiHandlers
         return new JetStreamApiResponse
         {
             StreamInfoList = page,
+            StreamNames = page.Select(s => s.Config.Name).ToList(),
             PaginationTotal = all.Count,
             PaginationOffset = offset,
         };

src/NATS.Server/JetStream/Api/JetStreamApiResponse.cs

@@ -77,6 +77,16 @@ public sealed class JetStreamApiResponse
         if (Error != null)
             return new { error = Error };
 
+        if (AccountInfo != null)
+        {
+            return new
+            {
+                type = "io.nats.jetstream.api.v1.account_info_response",
+                streams = AccountInfo.Streams,
+                consumers = AccountInfo.Consumers,
+            };
+        }
+
         if (StreamInfoList != null)
         {
             var wireStreams = StreamInfoList.Select(s => new