transfer compute shader

The retarget transfer: one invocation per output frame of a baked clip. It builds the source pose at that frame by forward kinematics over the clip's keys, gives each mapped target bone the source's anatomical frame carried from the source body onto the target body, and writes the target's local rotations channel after channel, with the pelvis and root translation and the frame's time. modules/retarget builds its buffers and reads the result back into a clip.