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/widget/taskview/taskview.h

@@ -44,26 +44,26 @@ public:
 	TaskView(QWidget *parent);
 
 signals:
-	void task_cancelled(Task *t);
+	void task_cancelled(OakEngineTask *t);
 
 public slots:
 	/**
-   * @brief Creates a TaskViewItem, connects it to a Task, and adds it to this widget
-   *
-   * Connect this to TaskManager::TaskAdded().
-   */
-	void add_task(Task *t);
+    * @brief Creates a TaskViewItem, connects it to a Task, and adds it to this widget
+    *
+    * Connect this to TaskManager::TaskAdded().
+    */
+	void add_task(OakEngineTask *t);
 
-	void task_failed(Task *t);
+	void task_failed(OakEngineTask *t);
 
-	void remove_task(Task *t);
+	void remove_task(OakEngineTask *t);
 
 private:
 	QWidget *central_widget_;
 
 	QVBoxLayout *layout_;
 
-	QHash<Task *, TaskViewItem *> items_;
+	QHash<OakEngineTask *, TaskViewItem *> items_;
 };
 
 }