R8: finish app/ pure C ABI migration (P3-P9) and make OTIO required

- app/ no longer includes engine C++ headers nor holds engine C++ types:
  engine access goes through the oakengine C ABI plus C++ wrappers
  (oakutil/oaknode.h, oakutil/oakvideo.h) and app-local mirror types
  (tooltypes, trackreferencehandle, timelinecommonapp, keyframetypes,
  subtitleapp, serializedlayoutinfoapp, nodevaluehandle, sliderdisplaytypeapp)
- engine: new C ABI functions for block/track/clip/transition navigation
  and predicates, links, caches, waveform/playback, disk folder,
  sequence_track_list, node_free, footage_is_valid, block_get_track,
  get_brush; loadotio/saveotio ported to the current engine API
- OTIO is now a required dependency: CI and CD build it on every
  platform, FindOpenTimelineIO fixed for OTIO 0.16/0.19 (the old deps
  include requirement silently disabled OTIO everywhere), runtime
  libraries are bundled into packages and copied next to macOS binaries
  (oak_copy_otio_runtime)
- fix ProjectViewModel drag&drop mime read/write size mismatch (segfault)
- unify color label naming (k_olive -> "Oak") in the app-side mirror
- docs: OTIO required, FFmpeg minimum corrected to 6.0 (en/zh)
- gtest suite: 1925 passed, 0 failed

tests/gtest/render_processor_test.cpp

@@ -678,11 +678,11 @@ TEST(ManagedColor, ColorInputAndOutputRoundTrip)
 	color.set_color_input(QStringLiteral("linear"));
 	EXPECT_EQ(color.color_input(), QStringLiteral("linear"));
 
-	color.set_color_output(olive::ColorTransform(QStringLiteral("sRGB")));
+	color.set_color_output(oak::ColorTransform(QStringLiteral("sRGB")));
 	EXPECT_FALSE(color.color_output().is_display());
 	EXPECT_EQ(color.color_output().output(), QStringLiteral("sRGB"));
 
-	color.set_color_output(olive::ColorTransform(QStringLiteral("sRGB"),
+	color.set_color_output(oak::ColorTransform(QStringLiteral("sRGB"),
 												 QStringLiteral("Filmic"),
 												 QStringLiteral("None")));
 	EXPECT_TRUE(color.color_output().is_display());