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

core/CMakeLists.txt

@@ -74,6 +74,10 @@ set_target_properties(olivecore PROPERTIES
 # OAKCORE_BUILD marks the library side of the export macros (dllexport)
 target_compile_definitions(olivecore PRIVATE OAKCORE_BUILD)
 
+if (COMMAND oak_copy_otio_runtime)
+  oak_copy_otio_runtime(olivecore)
+endif()
+
 # Export only the C ABI (oakcore_*), nothing else — not even symbols from
 # statically linked runtime libraries
 if (UNIX AND NOT APPLE)

core/src/oliveimpl/util/rational.h

@@ -98,7 +98,7 @@ public:
 	static Rational fromRationalTime(const opentime::RationalTime &t)
 	{
 		// Is this the best way to do this?
-		return fromDouble(t.to_seconds());
+		return from_double(t.to_seconds());
 	}
 
 	// Convert Olive rationals to opentime rationals with the given framerate (defaults to 24)