[bug-maybe] repair fixes broken shield


#1

Perhaps not technically a bug, but feels a bit overly stupid for automatic repair bots to attempt to repair shields once the shields are down, rather than other damaged units (especially since repair systems now have limited resources). Maybe shields that have been brought down and no longer functional should have the shield generator completely destroyed, which would also reinforce the fact that shields that have been brought down via damage (rather than stability) won’t be coming back.