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/curvewidget/curvewidget.cpp

@@ -30,6 +30,7 @@
 #include "core.h"
 #include "common/qtutils.h"
 #include "node/node.h"
+#include "common/nodevaluehandle.h"
 #include "oakengine/node.h"
 #include "widget/timeruler/timeruler.h"
 
@@ -275,7 +276,7 @@ void CurveWidget::connect_input_internal(Node *node, const QString &input,
 {
 	NodeInput input_ref(node, input, element);
 	int track_count =
-		NodeValue::get_number_of_keyframe_tracks(input_ref.get_data_type());
+		oakengine_node_value_keyframe_track_count(node_value_type_to_c(input_ref.get_data_type()));
 	for (int i = 0; i < track_count; i++) {
 		NodeKeyframeTrackReference track_ref(input_ref, i);
 		view_->connect_input(track_ref);