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/sequence/sequence.h

@@ -26,10 +26,11 @@
 #include <QDialog>
 #include <QSpinBox>
 
-#include "node/project/sequence/sequence.h"
 #include "sequencedialogparametertab.h"
 #include "sequencedialogpresettab.h"
 
+struct OakEngineNode;
+
 namespace olive
 {
 
@@ -67,7 +68,7 @@ public:
    * @param parent
    * QWidget parent
    */
-	SequenceDialog(Sequence *s, Type t = k_existing, QWidget *parent = nullptr);
+	SequenceDialog(OakEngineNode *s, Type t = k_existing, QWidget *parent = nullptr);
 
 	/**
    * @brief Set whether the parameter changes should be made into an undo command or not
@@ -90,7 +91,7 @@ public slots:
 	virtual void accept() override;
 
 private:
-	Sequence *sequence_;
+	OakEngineNode *sequence_;
 
 	SequenceDialogPresetTab *preset_tab_;