refactor: invert the last engine-to-UI dependencies

- NodeFactory's menu creation moves to UI-side widget/menu/factorymenu
  (the factory only exposes its node library read-only now)
- DiskManager's cache-settings dialog is created through a registered
  std::function handler (registered by Core at startup)
- OlivePluginInstance creates progress UIs through a
  PluginProgressReporter interface (Null fallback headless) and queries
  the active viewer through a provider callback, both registered by Core
- factory.h, diskmanager and pluginSupport no longer reference any
  widget//dialog//panel//window headers or classes

app/render/diskmanager.h

@@ -27,6 +27,8 @@
 #include <QObject>
 #include <QTimer>
 
+#include <functional>
+
 #include "common/define.h"
 #include "node/project.h"
 
@@ -143,6 +145,19 @@ public:
 
 	static QString get_default_disk_cache_path();
 
+	/**
+	 * @brief Handler showing the disk cache settings dialog for a folder
+	 *
+	 * Registered by the UI layer (e.g. a DiskCacheDialog-based
+	 * implementation), since the engine cannot show dialogs itself. Without
+	 * a handler, the request is logged and skipped.
+	 */
+	using ShowDiskCacheSettingsHandler =
+		std::function<void(DiskCacheFolder *folder, QWidget *parent)>;
+
+	static void set_show_disk_cache_settings_handler(
+		ShowDiskCacheSettingsHandler handler);
+
 	void show_disk_cache_settings_dialog(DiskCacheFolder *folder, QWidget *parent);
 	void show_disk_cache_settings_dialog(const QString &path, QWidget *parent);
 
@@ -165,6 +180,8 @@ private:
 
 	static DiskManager *instance_;
 
+	static ShowDiskCacheSettingsHandler show_disk_cache_settings_handler_;
+
 	QVector<DiskCacheFolder *> open_folders_;
 };