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

app/widget/colorbutton/colorbutton.cpp

@@ -61,7 +61,7 @@ void ColorButton::set_color(const ManagedColor &c)
 	color_.set_color_input(compliant_in);
 
 	QByteArray out_name = color_.color_output().output().toUtf8();
-	ColorTransform cs_out = color_.color_output();
+	oak::ColorTransform cs_out = color_.color_output();
 	QByteArray o, v, l;
 	oak_color_transform pod = oak_to_transform(cs_out, &o, &v, &l);
 	int out_is_display = 0;
@@ -70,11 +70,11 @@ void ColorButton::set_color(const ManagedColor &c)
 		color_manager_, &pod, 0, &out_is_display, out_buf, sizeof(out_buf),
 		view_buf, sizeof(view_buf), look_buf, sizeof(look_buf));
 	if (out_is_display) {
-		color_.set_color_output(ColorTransform(QString::fromUtf8(out_buf),
+		color_.set_color_output(oak::ColorTransform(QString::fromUtf8(out_buf),
 											   QString::fromUtf8(view_buf),
 											   QString::fromUtf8(look_buf)));
 	} else {
-		color_.set_color_output(ColorTransform(QString::fromUtf8(out_buf)));
+		color_.set_color_output(oak::ColorTransform(QString::fromUtf8(out_buf)));
 	}
 
 	update_color();
@@ -113,7 +113,7 @@ void ColorButton::color_dialog_finished(int e)
 void ColorButton::update_color()
 {
 	QByteArray in_cs = color_.color_input().toUtf8();
-	ColorTransform out = color_.color_output();
+	oak::ColorTransform out = color_.color_output();
 	QByteArray o, v, l;
 	oak_color_transform out_pod = oak_to_transform(out, &o, &v, &l);
 	color_processor_ = ColorProcessorHandlePtr(