Centralize legacy document open bridge

src/legacy_document_open_services.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include "app_core/document_session.h"
+#include "foundation/result.h"
+
+class App;
+
+namespace pp::panopainter {
+
+[[nodiscard]] pp::foundation::Status execute_legacy_document_open_plan(
+    App& app,
+    pp::app::DocumentOpenPlanAction action,
+    const pp::app::DocumentOpenRoute& route);
+
+} // namespace pp::panopainter