style: unify identifier naming per updated conventions

Automated with clang-tidy readability-identifier-naming (config added to
.clang-tidy) plus scripted passes, per the updated rules now documented
in CONTRIBUTING.md:

- types (class/struct/enum/alias/template params): PascalCase
- functions, variables, members: snake_case (incl. rational -> Rational)
- private/protected members: trailing underscore; static member
  variables likewise (instance_, available_themes_)
- constants and enum values: snake_case (kLinear -> k_linear,
  F32P -> f32p); ALL_CAPS reserved for macros
- macros: OAK_ prefix (OLIVE_ADD_TEST/OLIVE_ASSERT/OLIVE_CONFIG ->
  OAK_ADD_TEST/OAK_ASSERT/OAK_CONFIG, GL_PREAMBLE -> OAK_GL_PREAMBLE,
  include guards -> OAK_*)
- file names: all lowercase (Current/Plugin/OliveHost/OliveClip/
  OlivePluginInstance -> current/plugin/olivehost/oliveclip/
  oliveplugininstance)
- getters share the member name sans underscore, setters set_foo()
- Qt and third-party (OpenFX) virtual overrides and framework callbacks
  keep their original names (exempt in .clang-tidy)

Manual follow-ups required where automation could not reach:
- string-based QMetaObject/SIGNAL/SLOT references updated to renamed
  methods (AddTask, CreatedFile, DeleteSpecificFile, moveSelectionUp, ...)
- macro bodies referencing renamed methods (OLIVE_CONFIG,
  NODE_DEFAULT_DESTRUCTOR, MANAGEDDISPLAYWIDGET_*)
- self-shadowing locals renamed where signals/methods became same-named
  (size_changed, worker_count, selected_items, import param, filters)
- third_party OFX member/namespace usages restored (OFX::Host::*,
  _created, _clipPrefsDirty, createInstance, clearPersistentMessage)
- STL protocol aliases restored (const_iterator) with .clang-tidy
  ignore rules; qHash overloads restored

Full build and test suite pass: ctest 4/4, ~1960 gtest cases green.

app/widget/filefield/lutfilefield.cpp

@@ -35,7 +35,7 @@ LutFileField::LutFileField(QWidget *parent) : FileField(parent)
 	library_combo_->setMinimumContentsLength(12);
 	static_cast<QHBoxLayout *>(layout())->insertWidget(0, library_combo_, 1);
 
-	RefreshLibraryEntries();
+	refresh_library_entries();
 
 	connect(library_combo_,
 			static_cast<void (QComboBox::*)(int)>(&QComboBox::activated), this,
@@ -43,33 +43,33 @@ LutFileField::LutFileField(QWidget *parent) : FileField(parent)
 				const QString path =
 					library_combo_->itemData(index).toString();
 				if (!path.isEmpty()) {
-					SetFilename(path);
-					emit FilenameChanged(path);
+					set_filename(path);
+					emit filename_changed(path);
 				}
 			});
 
 	// Keep the combo in sync when the path is edited directly
-	connect(this, &FileField::FilenameChanged, this, [this](const QString &) {
-		RefreshLibraryEntries();
+	connect(this, &FileField::filename_changed, this, [this](const QString &) {
+		refresh_library_entries();
 	});
 }
 
-void LutFileField::SetFilename(const QString &s)
+void LutFileField::set_filename(const QString &s)
 {
-	FileField::SetFilename(s);
-	RefreshLibraryEntries();
+	FileField::set_filename(s);
+	refresh_library_entries();
 }
 
-void LutFileField::RefreshLibraryEntries()
+void LutFileField::refresh_library_entries()
 {
-	const QString current = GetFilename();
+	const QString current = get_filename();
 
 	const QSignalBlocker blocker(library_combo_);
 	library_combo_->clear();
 	library_combo_->addItem(tr("Other (Custom File)..."), QString());
 
-	const QStringList library_dirs = LUTLibrary::GetDirectories();
-	const QStringList luts = LUTLibrary::GetLutFiles();
+	const QStringList library_dirs = LUTLibrary::get_directories();
+	const QStringList luts = LUTLibrary::get_lut_files();
 	for (const QString &lut : luts) {
 		// Show the path relative to the library directory that contains it
 		QString display = lut;