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/timeline/timelinecoordinate.cpp

@@ -0,0 +1,67 @@
+/***
+
+  Olive - Non-Linear Video Editor
+  Copyright (C) 2022 Olive Team
+  Modifications Copyright (C) 2025 mikesolar
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#include "timelinecoordinate.h"
+
+namespace olive
+{
+
+TimelineCoordinate::TimelineCoordinate()
+	: track_(Track::k_none, 0)
+{
+}
+
+TimelineCoordinate::TimelineCoordinate(const Rational &frame,
+									   const Track::Reference &track)
+	: frame_(frame)
+	, track_(track)
+{
+}
+
+TimelineCoordinate::TimelineCoordinate(const Rational &frame,
+									   const Track::Type &track_type,
+									   const int &track_index)
+	: frame_(frame)
+	, track_(track_type, track_index)
+{
+}
+
+const Rational &TimelineCoordinate::get_frame() const
+{
+	return frame_;
+}
+
+const Track::Reference &TimelineCoordinate::get_track() const
+{
+	return track_;
+}
+
+void TimelineCoordinate::set_frame(const Rational &frame)
+{
+	frame_ = frame;
+}
+
+void TimelineCoordinate::set_track(const Track::Reference &track)
+{
+	track_ = track;
+}
+
+}