Is the prostration of forgetfulness obligatory for a latecomer to prayer who, having forgotten, turned to his right to say the taslim, then remembered and stood up to complete his prayer?

Turning to the right is a slight movement that does not necessitate a prostration of forgetfulness (sujud al-sahw). Your prayer is valid, and you do not need to repeat it. Superfluous actions in prayer are of two types: actions that are of the same kind as the prayer, which invalidate the prayer if done intentionally but require a prostration of forgetfulness if done out of forgetfulness; and actions that are not of the same kind as the prayer, which invalidate the prayer if done excessively but are excused if done slightly, and do not require a prostration of forgetfulness.