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/codec/frame.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef FRAME_H
-#define FRAME_H
+#ifndef OAK_FRAME_H
+#define OAK_FRAME_H
 
 #include <memory>
 #include <olive/core/core.h>
@@ -46,12 +46,12 @@ public:
 
 	DISABLE_COPY_MOVE(Frame)
 
-	static FramePtr Create();
+	static FramePtr create();
 
 	const VideoParams &video_params() const;
 	void set_video_params(const VideoParams &params);
 
-	static FramePtr Interlace(FramePtr top, FramePtr bottom);
+	static FramePtr interlace(FramePtr top, FramePtr bottom);
 
 	static int generate_linesize_bytes(int width, PixelFormat format,
 									   int channel_count);
@@ -93,14 +93,14 @@ public:
 	/**
    * @brief Get frame's timestamp.
    *
-   * This timestamp is always a rational that will equate to the time in seconds.
+   * This timestamp is always a Rational that will equate to the time in seconds.
    */
-	const rational &timestamp() const
+	const Rational &timestamp() const
 	{
 		return timestamp_;
 	}
 
-	void set_timestamp(const rational &timestamp)
+	void set_timestamp(const Rational &timestamp)
 	{
 		timestamp_ = timestamp;
 	}
@@ -161,7 +161,7 @@ private:
 	char *data_;
 	int data_size_;
 
-	rational timestamp_;
+	Rational timestamp_;
 
 	int linesize_;
 
@@ -172,4 +172,4 @@ private:
 
 Q_DECLARE_METATYPE(olive::FramePtr)
 
-#endif // FRAME_H
+#endif // OAK_FRAME_H