After conquering a city, army should be placed on city center

Right now, after you conquer a city, the city flips to you and your armies stay where they were when the battle started.

This can cause a series of "insta-flips" where you and an opponent capture a completely undefended city back and forth on the same turn, because there's no one actually in the city to defend it.

If the conquering army moved inside the city automatically, this would alleviate this problem.