refactor(undo): switch oakundo to refcounted value handles, migrate consumers
- OakUndoCommand/OakUndoStack become neutral by-value handles
{ctx, addref, release, abi_version}; a handle is a shared_ptr
equivalent at the ABI level, internals untouched (box owns/observes
flag; containers adopt, boxes created by factories own)
- oaknode command factories and undoable variants return/write value
handles; timeline command classes hold value handles; task import
take_command returns a value handle
- tests updated everywhere; suites green: oakundo 22, oaktimeline 117,
oaktask 106, oaknode 96, oakrender 44, oakcodec 18, oakcommon 193,
oakaudio 36
Mike-Solar
295ea1bfe5