app: migrate all engine access to the C ABI facade (nm U _ZN5olive = 0)

Every app module now reaches liboakengine exclusively through
oakengine_* C calls, EngineEventBridge subscriptions and app-side
handle headers (cliphandle/keyframehandle/nodevaluehandle/oakvaluehelper).
Direct C++ command construction, engine signal connect()s, and engine
type usage in MOC-visible signatures are gone: 557 -> 0 undefined
olive:: symbols in oak-editor.

app/dialog/progress/pluginprogressdialogreporter.h

@@ -40,7 +40,6 @@ class ProgressDialog;
  * is destroyed by the engine with deleteLater().
  */
 class PluginProgressDialogReporter : public plugin::PluginProgressReporter {
-	Q_OBJECT
 public:
 	PluginProgressDialogReporter(const QString &message, const QString &title);
 
@@ -52,8 +51,11 @@ public:
 
 	virtual void close() override;
 
+	bool was_cancelled() const { return cancelled_; }
+
 private:
 	QPointer<ProgressDialog> dialog_;
+	bool cancelled_ = false;
 };
 
 }