Hey there, thanks for playing!
The game pausing itself while on the background was a bug I thought I had fixed earlier, but someone notified me of the issue just after publishing the game... It will be fixed in the update that will come out in a few days!
The placing of already discovered items their recipe is already in the game! Right clicking should do exactly this! Seeing that I have a mobile version in mind too, I might change this in the future to support getting dragged into the output slot. Thanks for the idea!