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/common/html.cpp

@@ -275,7 +275,7 @@ void Html::write_char_format(QString *style, const QTextCharFormat &fmt)
 	}
 
 	if (fmt.foreground().style() != Qt::NoBrush) {
-		const QColor &color = fmt.foreground().color();
+		const QColor color = fmt.foreground().color();
 		QString cs;
 
 		if (color.alpha() == 255) {

engine/common/memorypool.h

@@ -225,7 +225,7 @@ public:
 		~Arena()
 		{
 			std::list<Element *> copy = lent_elements_;
-			foreach (Element *e, copy) {
+			for (Element *e : copy) {
 				e->release();
 			}
 
@@ -348,7 +348,7 @@ public:
 		QMutexLocker locker(&lock_);
 
 		// Attempt to get an element from an arena
-		foreach (Arena *a, arenas_) {
+		for (Arena *a : arenas_) {
 			ElementPtr e = a->Get();
 
 			if (e) {

engine/common/oiioutils.cpp

@@ -49,6 +49,10 @@ PixelFormat OIIOUtils::get_format_from_oiio_basetype(OIIO::TypeDesc::BASETYPE ty
 	switch (type) {
 	case OIIO::TypeDesc::UNKNOWN:
 	case OIIO::TypeDesc::NONE:
+#if OIIO_VERSION >= 20500
+	case OIIO::TypeDesc::USTRINGHASH:
+#endif
+	default:
 		break;
 
 	case OIIO::TypeDesc::INT8: