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).

tests/gtest/dynamic_render_backend_test.cpp

@@ -372,9 +372,11 @@ TEST(DynamicRenderBackend, VulkanIterativeBlitPingPong)
 	QByteArray dst_data(k_size * k_size * 4, 0);
 	dst->download(dst_data.data(), k_size);
 
-	// After two halving passes, red is 255 * 0.5 * 0.5. UNORM conversion floors
-	// the intermediate value, so the result is 63 rather than 64.
-	EXPECT_EQ(static_cast<uint8_t>(dst_data[0]), 63u);
+	// After two halving passes, red is 255 * 0.5 * 0.5. UNORM conversion may
+	// floor (63) or round-to-nearest (64) depending on the driver (llvmpipe
+	// rounds); both are spec-conformant.
+	const uint8_t red = static_cast<uint8_t>(dst_data[0]);
+	EXPECT_TRUE(red == 63u || red == 64u) << "red = " << int(red);
 	EXPECT_EQ(static_cast<uint8_t>(dst_data[1]), 0u);
 	EXPECT_EQ(static_cast<uint8_t>(dst_data[2]), 0u);
 	EXPECT_EQ(static_cast<uint8_t>(dst_data[3]), 255u);