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/codec/imagesection.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef IMAGESECTION_H
-#define IMAGESECTION_H
+#ifndef OAK_IMAGESECTION_H
+#define OAK_IMAGESECTION_H
 
 #include <QCheckBox>
 
@@ -35,33 +35,33 @@ class ImageSection : public CodecSection {
 public:
 	ImageSection(QWidget *parent = nullptr);
 
-	bool IsImageSequenceChecked() const
+	bool is_image_sequence_checked() const
 	{
 		return image_sequence_checkbox_->isChecked();
 	}
 
-	void SetImageSequenceChecked(bool e)
+	void set_image_sequence_checked(bool e)
 	{
 		image_sequence_checkbox_->setChecked(e);
 	}
 
-	void SetTimebase(const rational &r)
+	void set_timebase(const Rational &r)
 	{
-		frame_slider_->SetTimebase(r);
+		frame_slider_->set_timebase(r);
 	}
 
-	rational GetTime() const
+	Rational get_time() const
 	{
-		return frame_slider_->GetValue();
+		return frame_slider_->get_value();
 	}
 
-	void SetTime(const rational &t)
+	void set_time(const Rational &t)
 	{
-		frame_slider_->SetValue(t);
+		frame_slider_->set_value(t);
 	}
 
 signals:
-	void TimeChanged(const rational &t);
+	void time_changed(const Rational &t);
 
 private:
 	QCheckBox *image_sequence_checkbox_;
@@ -69,9 +69,9 @@ private:
 	RationalSlider *frame_slider_;
 
 private slots:
-	void ImageSequenceCheckBoxToggled(bool e);
+	void image_sequence_check_box_toggled(bool e);
 };
 
 }
 
-#endif // IMAGESECTION_H
+#endif // OAK_IMAGESECTION_H