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/audio/volume/volume.cpp

@@ -0,0 +1,109 @@
+/***
+
+  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 "volume.h"
+
+#include "node/sliderdisplaytype.h"
+
+namespace olive
+{
+
+const QString VolumeNode::k_samples_input = QStringLiteral("samples_in");
+const QString VolumeNode::k_volume_input = QStringLiteral("volume_in");
+
+#define super MathNodeBase
+
+VolumeNode::VolumeNode()
+{
+	add_input(k_samples_input, NodeValue::k_samples,
+			 InputFlags(k_input_flag_not_keyframable));
+
+	add_input(k_volume_input, NodeValue::k_float, 1.0);
+	set_input_property(k_volume_input, QStringLiteral("min"), 0.0);
+	set_input_property(k_volume_input, QStringLiteral("view"),
+					 slider::k_decibel);
+
+	set_flag(k_audio_effect);
+	set_effect_input(k_samples_input);
+}
+
+QString VolumeNode::name() const
+{
+	return tr("Volume");
+}
+
+QString VolumeNode::id() const
+{
+	return QStringLiteral("org.olivevideoeditor.Olive.volume");
+}
+
+QVector<Node::CategoryID> VolumeNode::category() const
+{
+	return { k_category_filter };
+}
+
+QString VolumeNode::description() const
+{
+	return tr("Adjusts the volume of an audio source.");
+}
+
+void VolumeNode::value(const NodeValueRow &value, const NodeGlobals &globals,
+					   NodeValueTable *table) const
+{
+	// Create a sample job
+	SampleBuffer buffer = value[k_samples_input].to_samples();
+
+	if (buffer.is_allocated()) {
+		// If the input is static, we can just do it now which will be faster
+		if (is_input_static(k_volume_input)) {
+			auto volume = value[k_volume_input].to_double();
+
+			if (!qFuzzyCompare(volume, 1.0)) {
+				buffer.transform_volume(volume);
+			}
+
+			table->push(NodeValue::k_samples, QVariant::fromValue(buffer), this);
+		} else {
+			// Requires job
+			SampleJob job(globals.time(), k_samples_input, value);
+			job.insert(k_volume_input, value);
+			table->push(NodeValue::k_samples, QVariant::fromValue(job), this);
+		}
+	}
+}
+
+void VolumeNode::process_samples(const NodeValueRow &values,
+								const SampleBuffer &input, SampleBuffer &output,
+								int index) const
+{
+	return process_samples_internal(values, k_op_multiply, k_samples_input,
+								  k_volume_input, input, output, index);
+}
+
+void VolumeNode::retranslate()
+{
+	super::retranslate();
+
+	set_input_name(k_samples_input, tr("Samples"));
+	set_input_name(k_volume_input, tr("Volume"));
+}
+
+}