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/timelinewidget/tool/beam.cpp

@@ -30,19 +30,19 @@ BeamTool::BeamTool(TimelineWidget *parent)
 {
 }
 
-void BeamTool::HoverMove(TimelineViewMouseEvent *event)
+void BeamTool::hover_move(TimelineViewMouseEvent *event)
 {
-	parent()->SetViewBeamCursor(
-		ValidatedCoordinate(event->GetCoordinates(true)));
+	parent()->set_view_beam_cursor(
+		validated_coordinate(event->get_coordinates(true)));
 }
 
-TimelineCoordinate BeamTool::ValidatedCoordinate(TimelineCoordinate coord)
+TimelineCoordinate BeamTool::validated_coordinate(TimelineCoordinate coord)
 {
 	if (Core::instance()->snapping()) {
-		rational movement;
-		parent()->SnapPoint({ coord.GetFrame() }, &movement);
+		Rational movement;
+		parent()->snap_point({ coord.get_frame() }, &movement);
 		if (!movement.isNull()) {
-			coord.SetFrame(coord.GetFrame() + movement);
+			coord.set_frame(coord.get_frame() + movement);
 		}
 	}