What is the ruling on a government employee executing a project belonging to his employing entity through his private company, and is it permissible for him to waive his salary and take unpaid leave to do so?

Those responsible for the tender in the company must choose the best offers that benefit the entity they work for, in terms of quality of work, specifications, and the lowest prices, without considering the needs of the applicants. If the project is awarded to the questioner's company, there is no objection to him accepting the project, provided that his work on it is outside official working hours or during his vacation, because his benefits during working hours belong to the entity he works for.