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.cpp

@@ -31,8 +31,10 @@ PluginProgressDialogReporter::PluginProgressDialogReporter(
 	: dialog_(new ProgressDialog(message, title, nullptr))
 {
 	dialog_->setAttribute(Qt::WA_DeleteOnClose);
-	connect(dialog_, &ProgressDialog::cancelled, this,
-			&PluginProgressReporter::cancelled);
+	QObject::connect(dialog_, &ProgressDialog::cancelled, dialog_, [this]() {
+		cancelled_ = true;
+		set_cancelled();
+	});
 }
 
 PluginProgressDialogReporter::~PluginProgressDialogReporter()