Add border styling for buttons in SelectablePagePageList component

apps/app/src/features/openai/client/components/AiAssistant/AiAssistantManagementModal/SelectablePagePageList.module.scss

@@ -6,6 +6,10 @@
   .list-group-item {
     border: none;
   }
+
+  .btn {
+    border: none;
+  }
 }
 
 // == Colors