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/projecttoolbar/projecttoolbar.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef PROJECTTOOLBAR_H
-#define PROJECTTOOLBAR_H
+#ifndef OAK_PROJECTTOOLBAR_H
+#define OAK_PROJECTTOOLBAR_H
 
 #include <QWidget>
 #include <QLineEdit>
@@ -44,26 +44,26 @@ class ProjectToolbar : public QWidget {
 public:
 	ProjectToolbar(QWidget *parent);
 
-	enum ViewType { TreeView, ListView, IconView };
+	enum ViewType { tree_view, list_view, icon_view };
 
 public slots:
-	void SetView(ViewType type);
+	void set_view(ViewType type);
 
 protected:
 	void changeEvent(QEvent *) override;
 
 signals:
-	void NewClicked();
-	void OpenClicked();
-	void SaveClicked();
+	void new_clicked();
+	void open_clicked();
+	void save_clicked();
 
-	void SearchChanged(const QString &);
+	void search_changed(const QString &);
 
-	void ViewChanged(ViewType type);
+	void view_changed(ViewType type);
 
 private:
-	void Retranslate();
-	void UpdateIcons();
+	void retranslate();
+	void update_icons();
 
 	QPushButton *new_button_;
 	QPushButton *open_button_;
@@ -76,9 +76,9 @@ private:
 	QPushButton *icon_button_;
 
 private slots:
-	void ViewButtonClicked();
+	void view_button_clicked();
 };
 
 }
 
-#endif // PROJECTTOOLBAR_H
+#endif // OAK_PROJECTTOOLBAR_H