build/ci: green builds and tests on all three platforms

Compiler hygiene (all platforms):
- Silence warnings across the tree: missing override, -Wreorder ctor
  init, -Wshadow, -Wsign-compare, missing switch cases, unused
  functions/captures, Qt 6.11 deprecations (QMouseEvent/QDropEvent
  accessors, qAsConst, Q_FOREACH over non-shared containers,
  AA_UseHighDpiPixmaps) and the .bak/ backup tree removal.
- Fix regressions from the cleanup: missing clip decls in
  capi/timeline.cpp, plugin.cpp rename fallout, panel setFocus
  ambiguity, QGraphicsItem::pos vs event->position(), duplicate
  k_push_button case, boolean test variable.

Windows:
- Qt portability: CommandLineParser is_set/add_option, QTimeZone
  systemTimeZone (QTimeZone::LocalTime is 6.11-only), k_progress_* enum.
- Linking: stop adding oakengine to OLIVE_LIBRARIES (import lib plus
  oakengine-obj caused multiple definitions); add OAKENGINE_STATIC so
  internal consumers no longer reference __imp_* stubs.
- oakengine.ver: export olive::Renderer typeinfo so liboakgl.so can be
  dlopened (Linux), DynamicRenderer no longer dlcloses backend libraries
  (crash in RenderManager's dtor calling into unmapped memory).
- OTIO runtime: copy DLLs next to every binary on Windows instead of
  relying on PATH (0xc0000135 in gtest discovery).
- Headless GL: the runner only has GDI OpenGL 1.1, killing every render
  worker. Deploy Mesa llvmpipe as opengl32sw.dll (Qt's software-GL
  channel) with QT_OPENGL=software, and let QT_OPENGL override the
  AA_UseDesktopOpenGL default. ExportTask fails fast after 8 consecutive
  undelivered frames instead of segfaulting or grinding forever;
  FFmpegEncoder::write_frame tolerates null frames.
- Tests: GetTempPathA+PID temp dirs, GetLongPathNameA for 8.3 names,
  forward-slash normalization when comparing project filenames.

Linux:
- Install libshaderc-dev so oakvulkan compiles GLSL (Vulkan tests).
- Accept UNORM floor-or-round (63/64) in the blit ping-pong test.
- Skip MainWindow construction test on the offscreen QPA (cannot paint
  QOpenGLWidget).

Also: oak_cli_transcode gets a 300s ctest timeout, worker logs GL
context version and LoadGraph/render_frame stages, and
docs/plans/eliminate-event-bridge-issues.md (English translation).

engine/node/plugins/plugin.cpp

@@ -232,8 +232,6 @@ QHash<QString, QVariant> build_default_values(
 			ofx_type == kOfxParamTypePushButton) {
 			continue;
 		}
-		const auto &props = param.second->getProperties();
-		bool is_secret = props.getIntProperty(kOfxParamPropSecret) != 0;
 		const QString input_id =
 			QString::fromStdString(param.second->getName());
 		if (input_id.isEmpty()) {
@@ -263,10 +261,10 @@ clip_label_for_name(const std::string &name,
 	}
 
 	if (desc) {
-		const std::string &label =
+		const std::string &param_label =
 			desc->getProps().getStringProperty(kOfxPropLabel);
-		if (!label.empty()) {
-			return QString::fromStdString(label);
+		if (!param_label.empty()) {
+			return QString::fromStdString(param_label);
 		}
 	}
 
@@ -432,9 +430,9 @@ olive::plugin::PluginNode::PluginNode(OFX::Host::ImageEffect::Instance *plugin)
 			const int value_count = props.getDimension(kOfxParamPropChoiceEnum);
 
 			for (int i = 0; i < label_count; ++i) {
-				const std::string &label =
+				const std::string &choice_label =
 					props.getStringProperty(kOfxParamPropChoiceOption, i);
-				option_labels.append(QString::fromStdString(label));
+				option_labels.append(QString::fromStdString(choice_label));
 			}
 
 			for (int i = 0; i < value_count; ++i) {

engine/node/plugins/plugin.h

@@ -62,7 +62,7 @@ public:
    */
 	virtual void process_samples(const NodeValueRow &values,
 								const SampleBuffer &input, SampleBuffer &output,
-								int index) const;
+								int index) const override;
 
 	/**
    * @brief If Value() pushes a GenerateJob, override this function for the image to create
@@ -71,7 +71,7 @@ public:
    *
    * The destination buffer. It will already be allocated and ready for writing to.
    */
-	virtual void generate_frame(FramePtr frame, const GenerateJob &job) const;
+	virtual void generate_frame(FramePtr frame, const GenerateJob &job) const override;
 
 private:
 	QString sub_category_;