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/nodeview/nodeviewscene.h

@@ -25,11 +25,9 @@
 #include <QGraphicsScene>
 #include <QTimer>
 
-#include "node/project.h"
 #include "nodeviewcontext.h"
 #include "nodeviewedge.h"
 #include "nodeviewitem.h"
-#include "undo/undostack.h"
 
 namespace olive
 {
@@ -44,7 +42,7 @@ public:
 
 	QVector<NodeViewItem *> get_selected_items() const;
 
-	const QHash<Node *, NodeViewContext *> &context_map() const
+	const QHash<oak::Node, NodeViewContext *> &context_map() const
 	{
 		return context_map_;
 	}
@@ -64,11 +62,9 @@ public:
 	}
 
 public:
-	// Not slots: signatures use the engine C++ type Node*, which must not be
-	// exposed to MOC (it would pull Node::staticMetaObject across the ABI
-	// boundary). They are called directly, never used as connect() targets.
-	NodeViewContext *add_context(Node *node);
-	void remove_context(Node *node);
+	// Not slots: they are called directly, never used as connect() targets.
+	NodeViewContext *add_context(oak::Node node);
+	void remove_context(oak::Node node);
 
 public slots:
 	/**
@@ -77,9 +73,7 @@ public slots:
 	void set_edges_are_curved(bool curved);
 
 private:
-	QHash<Node *, NodeViewContext *> context_map_;
-
-	Project *graph_;
+	QHash<oak::Node, NodeViewContext *> context_map_;
 
 	NodeViewCommon::FlowDirection direction_;