Does the brown blood spot, the size of a dirham with scattered dots, found at the time of the menstrual period, count as menstruation that prohibits prayer, or should one wait to see more blood?

The brownish discharge that precedes purification is not considered menstruation. It is only considered menstruation if it connects with blood at its end. If what you saw was not recognizable blood, then you are pure, and you must pray and fast. Even if it was recognizable blood, you are still pure, according to the majority of scholars, because the minimum duration of menstruation is one day and one night. If the bleeding stops before that, it is not considered menstruation, and you must pray.