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/common/hashstreamapp.cpp

@@ -0,0 +1,67 @@
+/***
+
+  Oak - Non-Linear Video Editor
+  Copyright (C) 2026 Oak Team
+
+  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/>.
+
+***/
+
+// App-side implementations of qHash overloads and stream operators
+// used by QHash containers and QDataStream serialization in app code.
+// Provides local definitions so the app doesn't import these from liboakengine.
+
+#include "node/param.h"
+#include "node/output/track/track.h"
+
+namespace olive
+{
+
+uint qHash(const NodeInput &i)
+{
+	return qHash(i.node()) ^ qHash(i.input()) ^ ::qHash(i.element());
+}
+
+uint qHash(const NodeInputPair &i)
+{
+	return qHash(i.node) ^ qHash(i.input);
+}
+
+uint qHash(const NodeKeyframeTrackReference &i)
+{
+	return qHash(i.input()) ^ ::qHash(i.track());
+}
+
+uint qHash(const Track::Reference &r, uint seed)
+{
+	return ::qHash(QStringLiteral("%1:%2").arg(QString::number(r.type()),
+											   QString::number(r.index())),
+				   seed);
+}
+
+QDataStream &operator<<(QDataStream &out, const Track::Reference &ref)
+{
+	out << static_cast<int>(ref.type()) << ref.index();
+	return out;
+}
+
+QDataStream &operator>>(QDataStream &in, Track::Reference &ref)
+{
+	int type, index;
+	in >> type >> index;
+	ref = Track::Reference(static_cast<Track::Type>(type), index);
+	return in;
+}
+
+}