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/panel/project/project.h

@@ -23,7 +23,6 @@
 #define OAK_PROJECT_PANEL_H
 
 #include "footagemanagementpanel.h"
-#include "node/project.h"
 #include "panel/panel.h"
 #include "widget/projectexplorer/projectexplorer.h"
 
@@ -41,22 +40,22 @@ public:
 	ProjectPanel(const QString &unique_name);
 	~ProjectPanel() override;
 
-	Project *project() const;
-	void set_project(Project *p);
+	oak::Project project() const;
+	void set_project(oak::Project p);
 
-	Folder *get_root() const;
+	oak::Node get_root() const;
 
-	void set_root(Folder *item);
+	void set_root(oak::Node item);
 
-	QVector<Node *> selected_items() const;
+	QVector<oak::Node> selected_items() const;
 
-	Folder *get_selected_folder() const;
+	oak::Node get_selected_folder() const;
 
 	virtual QVector<OakEngineNode *> get_selected_footage() const override;
 
 	ProjectViewModel *model() const;
 
-	bool select_item(Node *n, bool deselect_all_first = true)
+	bool select_item(oak::Node n, bool deselect_all_first = true)
 	{
 		return explorer_->select_item(n, deselect_all_first);
 	}