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/dialog/export/exportformatcombobox.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef EXPORTFORMATCOMBOBOX_H
-#define EXPORTFORMATCOMBOBOX_H
+#ifndef OAK_EXPORTFORMATCOMBOBOX_H
+#define OAK_EXPORTFORMATCOMBOBOX_H
 
 #include <QComboBox>
 #include <QWidgetAction>
@@ -36,19 +36,19 @@ class ExportFormatComboBox : public QComboBox {
 	Q_OBJECT
 public:
 	enum Mode {
-		kShowAllFormats,
-		kShowAudioOnly,
-		kShowVideoOnly,
-		kShowSubtitlesOnly
+		k_show_all_formats,
+		k_show_audio_only,
+		k_show_video_only,
+		k_show_subtitles_only
 	};
 
 	ExportFormatComboBox(Mode mode, QWidget *parent = nullptr);
 	ExportFormatComboBox(QWidget *parent = nullptr)
-		: ExportFormatComboBox(kShowAllFormats, parent)
+		: ExportFormatComboBox(k_show_all_formats, parent)
 	{
 	}
 
-	ExportFormat::Format GetFormat() const
+	ExportFormat::Format get_format() const
 	{
 		return current_;
 	}
@@ -56,24 +56,24 @@ public:
 	void showPopup();
 
 signals:
-	void FormatChanged(ExportFormat::Format fmt);
+	void format_changed(ExportFormat::Format fmt);
 
 public slots:
-	void SetFormat(ExportFormat::Format fmt);
+	void set_format(ExportFormat::Format fmt);
 
 private slots:
-	void HandleIndexChange(QAction *a);
+	void handle_index_change(QAction *a);
 
 private:
-	void PopulateType(Track::Type type);
+	void populate_type(Track::Type type);
 
-	QWidgetAction *CreateHeader(const QIcon &icon, const QString &title);
+	QWidgetAction *create_header(const QIcon &icon, const QString &title);
 
 	Menu *custom_menu_;
 
-	ExportFormat::Format current_ = ExportFormat::kFormatCount;
+	ExportFormat::Format current_ = ExportFormat::k_format_count;
 };
 
 }
 
-#endif // EXPORTFORMATCOMBOBOX_H
+#endif // OAK_EXPORTFORMATCOMBOBOX_H