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/dialog/progress/pluginprogressdialogreporter.cpp

@@ -33,8 +33,10 @@ PluginProgressDialogReporter::PluginProgressDialogReporter(
 	dialog_->setAttribute(Qt::WA_DeleteOnClose);
 	QObject::connect(dialog_, &ProgressDialog::cancelled, dialog_, [this]() {
 		cancelled_ = true;
-		set_cancelled();
 	});
+	// The engine's C adapter treats show() as a no-op, so the dialog is
+	// shown here at create time.
+	dialog_->show();
 }
 
 PluginProgressDialogReporter::~PluginProgressDialogReporter()
@@ -49,18 +51,4 @@ void PluginProgressDialogReporter::set_progress(double value)
 	}
 }
 
-void PluginProgressDialogReporter::show()
-{
-	if (dialog_) {
-		dialog_->show();
-	}
-}
-
-void PluginProgressDialogReporter::close()
-{
-	if (dialog_) {
-		dialog_->close();
-	}
-}
-
 }