Option: Always reserve stage manager space

[sbscan]

Rectangle respects Stage Manager, but this behavior is not very convenient. At the very least, it should be optional.
When there are no apps in Stage Manager, it occupies the whole screen. This leads to:

Inability to use Stage Manager smoothly due to lack of space.
Windows being arranged in different positions depending on the situation.

[rxhanson]

Thanks for the feedback. This isn’t a change I have plans to add in myself, but see no reason to turn down a good pull request that adds this as a configuration set via Terminal command (not in the UI).