Centralize legacy history bridge

src/legacy_history_services.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include "app_core/history_ui.h"
+#include "foundation/result.h"
+
+namespace pp::panopainter {
+
+struct LegacyHistorySnapshot {
+    int undo_count = 0;
+    int redo_count = 0;
+    int memory_bytes = 0;
+};
+
+[[nodiscard]] LegacyHistorySnapshot legacy_history_snapshot() noexcept;
+[[nodiscard]] pp::foundation::Status execute_legacy_history_plan(const pp::app::HistoryUiPlan& plan);
+void clear_legacy_history() noexcept;
+
+} // namespace pp::panopainter