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/multicam/multicamdisplay.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef MULTICAMDISPLAY_H
-#define MULTICAMDISPLAY_H
+#ifndef OAK_MULTICAMDISPLAY_H
+#define OAK_MULTICAMDISPLAY_H
 
 #include "node/input/multicam/multicamnode.h"
 #include "widget/viewer/viewerdisplay.h"
@@ -33,17 +33,17 @@ class MulticamDisplay : public ViewerDisplayWidget {
 public:
 	explicit MulticamDisplay(QWidget *parent = nullptr);
 
-	void SetMulticamNode(MultiCamNode *n);
+	void set_multicam_node(MultiCamNode *n);
 
 protected:
-	virtual void OnPaint() override;
+	virtual void on_paint() override;
 
-	virtual void OnDestroy() override;
+	virtual void on_destroy() override;
 
-	virtual TexturePtr LoadCustomTextureFromFrame(const QVariant &v) override;
+	virtual TexturePtr load_custom_texture_from_frame(const QVariant &v) override;
 
 private:
-	static QString GenerateShaderCode(int rows, int cols);
+	static QString generate_shader_code(int rows, int cols);
 
 	MultiCamNode *node_;
 
@@ -54,4 +54,4 @@ private:
 
 }
 
-#endif // MULTICAMDISPLAY_H
+#endif // OAK_MULTICAMDISPLAY_H