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/StreamManager.cs

@@ -565,15 +565,20 @@ public sealed class StreamManager : IDisposable
         if (existing.Storage != proposed.Storage)
             errors.Add("storage type cannot be changed");
 
-        // Mirror is immutable — if the existing stream has a mirror, the proposed must keep it.
+        // Mirror is immutable — if both have a mirror it must match. Clearing a mirror
+        // (promoting to normal stream) is allowed after the origin is deleted.
+        // Go reference: server/stream.go — update allows clearing mirror for promotion.
         if (!string.IsNullOrWhiteSpace(existing.Mirror)
+            && !string.IsNullOrWhiteSpace(proposed.Mirror)
             && !string.Equals(existing.Mirror, proposed.Mirror, StringComparison.Ordinal))
         {
             errors.Add("mirror configuration cannot be changed");
         }
 
-        // Sources are immutable after creation — the set of source names must be unchanged.
-        if (existing.Sources.Count > 0)
+        // Sources: changing to a different non-empty set is not allowed, but clearing
+        // sources (removing all) or adding sources to a previously source-less stream is permitted.
+        // Go reference: server/stream.go — update allows adding/removing sources.
+        if (existing.Sources.Count > 0 && proposed.Sources.Count > 0)
         {
             var existingNames = existing.Sources.Select(s => s.Name).OrderBy(n => n, StringComparer.Ordinal).ToList();
             var proposedNames = proposed.Sources.Select(s => s.Name).OrderBy(n => n, StringComparer.Ordinal).ToList();
@@ -592,10 +597,6 @@ public sealed class StreamManager : IDisposable
             errors.Add("max consumers can only be increased");
         }
 
-        // Replicas must be odd (for RAFT consensus).
-        if (proposed.Replicas > 1 && proposed.Replicas % 2 == 0)
-            errors.Add("replicas must be odd for RAFT consensus");
-
         // Subject overlap detection with peer streams.
         if (otherStreams is not null && proposed.Subjects.Count > 0)
         {