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/exportaudiotab.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef EXPORTAUDIOTAB_H
-#define EXPORTAUDIOTAB_H
+#ifndef OAK_EXPORTAUDIOTAB_H
+#define OAK_EXPORTAUDIOTAB_H
 
 #include <QComboBox>
 #include <QWidget>
@@ -38,13 +38,13 @@ class ExportAudioTab : public QWidget {
 public:
 	ExportAudioTab(QWidget *parent = nullptr);
 
-	ExportCodec::Codec GetCodec() const
+	ExportCodec::Codec get_codec() const
 	{
 		return static_cast<ExportCodec::Codec>(
 			codec_combobox_->currentData().toInt());
 	}
 
-	void SetCodec(ExportCodec::Codec c)
+	void set_codec(ExportCodec::Codec c)
 	{
 		for (int i = 0; i < codec_combobox_->count(); i++) {
 			if (codec_combobox_->itemData(i) == c) {
@@ -75,7 +75,7 @@ public:
 	}
 
 public slots:
-	int SetFormat(ExportFormat::Format format);
+	int set_format(ExportFormat::Format format);
 
 private:
 	ExportFormat::Format fmt_;
@@ -85,14 +85,14 @@ private:
 	SampleFormatComboBox *sample_format_combobox_;
 	IntegerSlider *bit_rate_slider_;
 
-	static const int kDefaultBitRate;
+	static const int k_default_bit_rate;
 
 private slots:
-	void UpdateSampleFormats();
+	void update_sample_formats();
 
-	void UpdateBitRateEnabled();
+	void update_bit_rate_enabled();
 };
 
 }
 
-#endif // EXPORTAUDIOTAB_H
+#endif // OAK_EXPORTAUDIOTAB_H