color: global LUT library, LUT error reporting, clamp + display fixes

- Add a global LUT library: user-configurable directories (new
  Preferences > LUT tab) scanned recursively for .cube/.3dl files; LUT
  node file pickers offer the library dirs as sidebar shortcuts via a
  'lut_library' input property handled by the param view bridge
- OCIOLutNode no longer fails silently: missing files, unsupported
  extensions and OCIO load errors are recorded in last_error() and
  surfaced in the status bar (input still passes through for rendering
  safety)
- ColorDialog: re-enable the display -> reference conversion using
  ColorProcessor::kInverse with a validity guard, and re-enable the
  Display tab in ColorValuesWidget; covered by a round-trip regression
  test proving the old OCIO inverse crash no longer occurs
- OCIOGradingTransformLinearNode: enforce the OCIO clampWhite >
  clampBlack invariant per frame in Value() so keyframed/connected
  values cannot produce invalid grading transforms, and constrain the
  white clamp UI minimum whenever the black clamp is static
- Regression tests for LUT extension checks, direction switching, node
  error reporting, LUT library scanning, display inverse round-trip and
  clamp enforcement

app/widget/colorwheel/colorvalueswidget.cpp

@@ -91,9 +91,6 @@ ColorValuesWidget::ColorValuesWidget(ColorManager *manager, QWidget *parent)
 		connect(display_tab_, &ColorValuesTab::ColorChanged, this,
 				&ColorValuesWidget::UpdateValuesFromDisplay);
 
-		// FIXME: Display -> Ref temporarily disabled due to OCIO crash (see ColorDialog::ColorSpaceChanged for more info)
-		display_tab_->setEnabled(false);
-
 		layout->addWidget(tabs);
 	}
 }

app/widget/filefield/filefield.cpp

@@ -24,6 +24,7 @@
 #include <QFileDialog>
 #include <QFileInfo>
 #include <QHBoxLayout>
+#include <QUrl>
 
 #include "ui/icons/icons.h"
 
@@ -56,11 +57,30 @@ void FileField::BrowseBtnClicked()
 {
 	QString s;
 
-	if (directory_mode_) {
-		s = QFileDialog::getExistingDirectory(this, tr("Open Directory"));
+	if (sidebar_urls_.isEmpty()) {
+		if (directory_mode_) {
+			s = QFileDialog::getExistingDirectory(this, tr("Open Directory"));
+		} else {
+			s = QFileDialog::getOpenFileName(this, tr("Open File"), QString(),
+											 name_filter_);
+		}
 	} else {
-		s = QFileDialog::getOpenFileName(this, tr("Open File"), QString(),
-										 name_filter_);
+		// Sidebar URLs require the non-static dialog API
+		QFileDialog dialog(this, tr("Open File"));
+		dialog.setFileMode(directory_mode_ ? QFileDialog::Directory :
+											 QFileDialog::ExistingFile);
+		dialog.setAcceptMode(QFileDialog::AcceptOpen);
+		if (!directory_mode_ && !name_filter_.isEmpty()) {
+			dialog.setNameFilter(name_filter_);
+		}
+		dialog.setSidebarUrls(sidebar_urls_);
+		if (directory_mode_) {
+			dialog.setOption(QFileDialog::ShowDirsOnly, true);
+		}
+
+		if (dialog.exec() == QDialog::Accepted && !dialog.selectedFiles().isEmpty()) {
+			s = dialog.selectedFiles().first();
+		}
 	}
 
 	if (!s.isEmpty()) {

app/widget/filefield/filefield.h

@@ -58,6 +58,17 @@ public:
 		name_filter_ = filter;
 	}
 
+	/**
+	 * @brief Sets extra sidebar shortcuts (e.g. a library directory) for the
+	 * browse dialog
+	 *
+	 * Note: setting sidebar URLs requires Qt's non-native file dialog.
+	 */
+	void SetSidebarUrls(const QList<QUrl> &urls)
+	{
+		sidebar_urls_ = urls;
+	}
+
 signals:
 	void FilenameChanged(const QString &filename);
 
@@ -70,6 +81,8 @@ private:
 
 	QString name_filter_;
 
+	QList<QUrl> sidebar_urls_;
+
 private slots:
 	void BrowseBtnClicked();
 

app/widget/nodeparamview/nodeparamviewwidgetbridge.cpp

@@ -23,6 +23,7 @@
 
 #include <QCheckBox>
 #include <QFontComboBox>
+#include <QUrl>
 #include <QVector2D>
 #include <QVector3D>
 #include <QVector4D>
@@ -36,6 +37,7 @@
 #include "node/project/sequence/sequence.h"
 #include "nodeparamviewarraywidget.h"
 #include "nodeparamviewtextedit.h"
+#include "render/lutlibrary.h"
 #include "undo/undostack.h"
 #include "widget/bezier/bezierwidget.h"
 #include "widget/colorbutton/colorbutton.h"
@@ -938,6 +940,16 @@ void NodeParamViewWidgetBridge::SetProperty(const QString &key,
 			ff->SetDirectoryMode(value.toBool());
 		} else if (key == QStringLiteral("filter")) {
 			ff->SetNameFilter(value.toString());
+		} else if (key == QStringLiteral("lut_library") && value.toBool()) {
+			// Offer the global LUT library directories as sidebar shortcuts in
+			// the browse dialog
+			QList<QUrl> sidebar_urls;
+			for (const QString &dir : LUTLibrary::GetDirectories()) {
+				sidebar_urls.append(QUrl::fromLocalFile(dir));
+			}
+			if (!sidebar_urls.isEmpty()) {
+				ff->SetSidebarUrls(sidebar_urls);
+			}
 		}
 	}