Require non-null References for batch rec action invoke

Enforce non-nullable References in RecActionController and InvokeBatchRecActionViewsCommand. Update tests to always provide References and add missing using directive. Improves type safety and ensures consistent reference handling.

src/ReC.Application/RecActions/Commands/InvokeBatchRecActionViewsCommand.cs

@@ -9,7 +9,7 @@ namespace ReC.Application.RecActions.Commands;
 public record InvokeBatchRecActionViewsCommand : IRequest
 {
     public long ProfileId { get; init; }
-    public InvokeReferences? References { get; init; }
+    public required InvokeReferences References { get; init; }
 }
 
 public class InvokeRecActionViewsCommandHandler(ISender sender, ILogger<InvokeRecActionViewsCommandHandler>? logger = null) : IRequestHandler<InvokeBatchRecActionViewsCommand>