Am I obligated to share the profits from additional work that was not included in the original agreement with my friend, and am I entitled to take a supervision allowance for the project in view of my additional effort, and does my friend's right to partnership extend to new work on the same project that is not related to the initial agreement?

It is permissible to take a fee for brokerage with a known percentage of the price, by agreement of both parties. The broker is only entitled to a fee for the work he brokered, for profit is earned through work, money, or guarantee. The broker is not entitled to claim more than that. Therefore, your friend is only entitled to what you both agreed upon regarding the first project. You are not allowed to take a salary for supervision under the pretext that it is for your extra work, because your friend's company is limited to brokerage, and anything beyond that is your responsibility, except for tasks that are not customarily performed by you, in which case you can hire workers to perform them. And you are obligated to fulfill what you have agreed upon.