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.cpp

@@ -22,7 +22,6 @@
 #include "nodeviewscene.h"
 
 #include "core.h"
-#include "node/project/sequence/sequence.h"
 #include "nodeviewedge.h"
 #include "nodeviewitem.h"
 
@@ -70,7 +69,7 @@ QVector<NodeViewItem *> NodeViewScene::get_selected_items() const
 	return items;
 }
 
-NodeViewContext *NodeViewScene::add_context(Node *node)
+NodeViewContext *NodeViewScene::add_context(oak::Node node)
 {
 	NodeViewContext *context_item = context_map_.value(node);
 
@@ -96,7 +95,7 @@ NodeViewContext *NodeViewScene::add_context(Node *node)
 	return context_item;
 }
 
-void NodeViewScene::remove_context(Node *node)
+void NodeViewScene::remove_context(oak::Node node)
 {
 	delete context_map_.take(node);
 }