Fixed empty assistant categories after hiding all their assistants (#902)

app/MindWork AI Studio/Components/IAssistantCategoryMember.cs

@@ -0,0 +1,16 @@
+namespace AIStudio.Components;
+
+/// <summary>
+/// Represents an assistant block which belongs to an assistant category.
+/// </summary>
+/// <remarks>
+/// Assistant blocks are generic over their settings dialog. This interface gives the category block
+/// access to their visibility without the need to know that type parameter.
+/// </remarks>
+public interface IAssistantCategoryMember
+{
+    /// <summary>
+    /// Gets whether the assistant is visible right now.
+    /// </summary>
+    bool IsVisible { get; }
+}