Centralize retained UI overlay insertion

src/legacy_ui_overlay_services.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include "foundation/result.h"
+
+#include <memory>
+
+class App;
+class Node;
+
+namespace pp::panopainter {
+
+void initialize_legacy_overlay_node(App& app, Node& node);
+
+[[nodiscard]] pp::foundation::Status attach_legacy_overlay_node(
+    App& app,
+    const std::shared_ptr<Node>& node) noexcept;
+
+template <class T>
+std::shared_ptr<T> make_legacy_overlay_node(App& app)
+{
+    auto node = std::make_shared<T>();
+    initialize_legacy_overlay_node(app, *node);
+    return node;
+}
+
+template <class T>
+std::shared_ptr<T> add_legacy_overlay_node(App& app)
+{
+    auto node = make_legacy_overlay_node<T>(app);
+    (void)attach_legacy_overlay_node(app, node);
+    return node;
+}
+
+} // namespace pp::panopainter