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

tests/gtest/project_factory_test.cpp

@@ -555,8 +555,11 @@ TEST(NodeFactory, CreateMenuWithNoneItem)
 		}
 		const QString id = olive::get_node_id_from_menu_action(leaf);
 		EXPECT_FALSE(id.isEmpty());
+		// create_node_from_menu_action returns an owned oak::Node handle;
+		// reinterpret it back to the engine type to take ownership
+		const oak::Node created_handle = olive::create_node_from_menu_action(leaf);
 		std::unique_ptr<olive::Node> node(
-			olive::create_node_from_menu_action(leaf));
+			reinterpret_cast<olive::Node *>(created_handle.handle()));
 		ASSERT_NE(node, nullptr);
 		EXPECT_EQ(node->id(), id);
 		++created;
@@ -571,7 +574,7 @@ TEST(NodeFactory, CreateMenuRestrictedToCategory)
 	olive::NodeFactory::initialize();
 
 	std::unique_ptr<olive::Menu> menu(olive::create_node_menu(
-		nullptr, false, olive::Node::k_category_math));
+		nullptr, false, oak::k_category_math));
 	ASSERT_NE(menu, nullptr);
 
 	QList<QAction *> leaves;
@@ -579,8 +582,9 @@ TEST(NodeFactory, CreateMenuRestrictedToCategory)
 	ASSERT_FALSE(leaves.isEmpty());
 
 	for (QAction *leaf : leaves) {
+		const oak::Node created_handle = olive::create_node_from_menu_action(leaf);
 		std::unique_ptr<olive::Node> node(
-			olive::create_node_from_menu_action(leaf));
+			reinterpret_cast<olive::Node *>(created_handle.handle()));
 		ASSERT_NE(node, nullptr);
 		EXPECT_TRUE(node->category().contains(olive::Node::k_category_math))
 			<< node->id().toStdString();