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/exportcodec.h

@@ -19,8 +19,8 @@
 
 ***/
 
-#ifndef EXPORTCODEC_H
-#define EXPORTCODEC_H
+#ifndef OAK_EXPORTCODEC_H
+#define OAK_EXPORTCODEC_H
 
 #include <QObject>
 #include <QString>
@@ -36,36 +36,36 @@ class ExportCodec : public QObject {
 public:
 	// Only append to this list (never insert) because indexes are used in serialized files
 	enum Codec {
-		kCodecDNxHD,
-		kCodecH264,
-		kCodecH264rgb,
-		kCodecH265,
-		kCodecOpenEXR,
-		kCodecPNG,
-		kCodecProRes,
-		kCodecCineform,
-		kCodecTIFF,
-		kCodecVP9,
-		kCodecMP2,
-		kCodecMP3,
-		kCodecAAC,
-		kCodecPCM,
-		kCodecOpus,
-		kCodecVorbis,
-		kCodecFLAC,
-		kCodecSRT,
-		kCodecAV1,
+		k_codec_d_nx_hd,
+		k_codec_h264,
+		k_codec_h264rgb,
+		k_codec_h265,
+		k_codec_open_exr,
+		k_codec_png,
+		k_codec_pro_res,
+		k_codec_cineform,
+		k_codec_tiff,
+		k_codec_v_p9,
+		k_codec_m_p2,
+		k_codec_m_p3,
+		k_codec_aac,
+		k_codec_pcm,
+		k_codec_opus,
+		k_codec_vorbis,
+		k_codec_flac,
+		k_codec_srt,
+		k_codec_a_v1,
 
-		kCodecCount
+		k_codec_count
 	};
 
-	static QString GetCodecName(Codec c);
+	static QString get_codec_name(Codec c);
 
-	static bool IsCodecAStillImage(Codec c);
+	static bool is_codec_a_still_image(Codec c);
 
-	static bool IsCodecLossless(Codec c);
+	static bool is_codec_lossless(Codec c);
 };
 
 }
 
-#endif // EXPORTCODEC_H
+#endif // OAK_EXPORTCODEC_H