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/otioproperties/otiopropertiesdialog.h

@@ -25,8 +25,9 @@
 
 #include "oakutil/define.h"
 #include "opentimelineio/timeline.h"
-#include "node/project/sequence/sequence.h"
-#include "node/project.h"
+
+struct OakEngineProject;
+struct OakEngineSequence;
 
 namespace olive
 {
@@ -39,13 +40,14 @@ namespace olive
 class OTIOPropertiesDialog : public QDialog {
 	Q_OBJECT
 public:
-	OTIOPropertiesDialog(const QList<Sequence *> &sequences,
-						 Project *active_project, QWidget *parent = nullptr);
+	OTIOPropertiesDialog(const QList<OakEngineSequence *> &sequences,
+						 OakEngineProject *active_project,
+						 QWidget *parent = nullptr);
 
 private:
 	QTreeWidget *table_;
 
-	const QList<Sequence *> sequences_;
+	const QList<OakEngineSequence *> sequences_;
 
 private slots:
 	/**