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).

app/main.cpp

@@ -228,7 +228,7 @@ int main(int argc, char *argv[])
 							 "main", "Decompress project file (No GUI)"));
 
 #ifdef _WIN32
-	auto console_option = parser.AddOption(
+	auto console_option = parser.add_option(
 		{ QStringLiteral("c"), QStringLiteral("-console") },
 		QCoreApplication::translate("main", "Launch with debug console"));
 #endif // _WIN32
@@ -333,15 +333,19 @@ int main(int argc, char *argv[])
 	// so far.
 	//
 	// https://bugreports.qt.io/browse/QTBUG-46140
-	QCoreApplication::setAttribute(Qt::AA_UseDesktopOpenGL);
+	// An explicit QT_OPENGL (e.g. "software" on GPU-less CI runners with
+	// Mesa deployed as opengl32sw.dll) takes precedence over this default.
+	if (!qEnvironmentVariableIsSet("QT_OPENGL")) {
+		QCoreApplication::setAttribute(Qt::AA_UseDesktopOpenGL);
+	}
 	format.setVersion(3, 2);
 	format.setProfile(QSurfaceFormat::CoreProfile);
 
 	format.setDepthBufferSize(24);
 	QSurfaceFormat::setDefaultFormat(format);
 
-	// Enable application automatically using higher resolution images from icons
-	QCoreApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+	// High-DPI pixmaps are always enabled in Qt 6 (AA_UseHighDpiPixmaps is
+	// deprecated and has no effect).
 
 	QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
 
@@ -352,7 +356,7 @@ int main(int argc, char *argv[])
 #ifdef _WIN32
 		// Since Oak Video Editor is linked with the console subsystem (for better POSIX compatibility), a console
 		// is created by default. If the user didn't request one, we free it here.
-		if (!console_option->IsSet()) {
+		if (!console_option->is_set()) {
 			FreeConsole();
 		}
 #endif // _WIN32