- new primitives: keyframes_set_time_many (conflict-safe batch time
move), keyframes_set_value_many (captured or explicit old values),
keyframes_set_bezier_many (double precision), and
keyframe_set_bezier_point (single handle with NaN-capture fallback)
- dialog and curveview drag finalization go through the facade; the
tests exercise the same global undo stack via oakengine_project_undo
- keyframeview/keyframeviewundo.{h,cpp} removed with zero remaining
references