build: split the engine into liboakengine.so; worker drops the UI entirely

Physical split: app/{audio,cli,codec,common,config,node,pluginSupport,
render,task,timeline,undo,tool,shaders} plus coreengine, version and
ui/icons+colorcoding move to a new top-level engine/ tree, built as
liboakengine.so (shared). The render backends (oakgl/oakvulkan) move
with it and link the engine library instead of embedding a static
render-core subset (libolive-rendercore is gone).

- oak-render-worker now links liboakengine instead of the whole
  libolive-editor object set: 336MB -> 2.9MB, no Qt Widgets UI
- the editor links liboakengine for the engine and keeps only UI
  objects in libolive-editor
- install/packaging: GNUInstallDirs libdir on Linux, bundle copy on
  macOS, oakengine.dll staged for NSIS, AppImage validation entry
- fix backend lookup for the new layout: DynamicRenderer searched
  ../app but backends now live in engine/; a stale pre-split liboakgl
  in the build tree got dlopened instead, re-initialized and later
  destroyed the interposed engine statics (full-suite segfault at
  DialogSequenceParameterTab, found via gdb watchpoint)

engine/node/time/timeoffset/timeoffsetnode.cpp

@@ -0,0 +1,96 @@
+/***
+
+  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 "timeoffsetnode.h"
+
+#include "node/sliderdisplaytype.h"
+
+namespace olive
+{
+
+const QString TimeOffsetNode::k_time_input = QStringLiteral("time_in");
+const QString TimeOffsetNode::k_input_input = QStringLiteral("input_in");
+
+#define super Node
+
+TimeOffsetNode::TimeOffsetNode()
+{
+	add_input(k_time_input, NodeValue::k_rational, QVariant::fromValue(Rational(0)),
+			 InputFlags(k_input_flag_not_connectable));
+	set_input_property(k_time_input, QStringLiteral("view"), slider::k_time);
+	set_input_property(k_time_input, QStringLiteral("viewlock"), true);
+
+	add_input(k_input_input, NodeValue::k_none,
+			 InputFlags(k_input_flag_not_keyframable));
+}
+
+void TimeOffsetNode::retranslate()
+{
+	super::retranslate();
+
+	set_input_name(k_time_input, QStringLiteral("Time"));
+	set_input_name(k_input_input, QStringLiteral("Input"));
+}
+
+TimeRange TimeOffsetNode::input_time_adjustment(const QString &input, int element,
+											  const TimeRange &input_time,
+											  bool clamp) const
+{
+	if (input == k_input_input) {
+		return TimeRange(get_remapped_time(input_time.in()),
+						 get_remapped_time(input_time.out()));
+	} else {
+		return super::input_time_adjustment(input, element, input_time, clamp);
+	}
+}
+
+TimeRange
+TimeOffsetNode::output_time_adjustment(const QString &input, int element,
+									 const TimeRange &input_time) const
+{
+	if (input == k_input_input) {
+		// The inverse of InputTimeAdjustment(): times at the input are mapped
+		// back to the output by subtracting the offset again
+		return TimeRange(get_remapped_output_time(input_time.in()),
+						 get_remapped_output_time(input_time.out()));
+	} else {
+		return super::output_time_adjustment(input, element, input_time);
+	}
+}
+
+void TimeOffsetNode::value(const NodeValueRow &value,
+						   const NodeGlobals &globals,
+						   NodeValueTable *table) const
+{
+	table->push(value[k_input_input]);
+}
+
+Rational TimeOffsetNode::get_remapped_time(const Rational &input) const
+{
+	return input + get_value_at_time(k_time_input, input).value<Rational>();
+}
+
+Rational TimeOffsetNode::get_remapped_output_time(const Rational &input) const
+{
+	return input - get_value_at_time(k_time_input, input).value<Rational>();
+}
+
+}