Added barracks healing and garrison recruitment

I made Barracks care for the infantry inside them, restoring six health points per second up to full health. Core buildings and carriers do not receive this healing behavior.

RECRUITS switches between field deployment and the garrison. A full sixteen-seat building holds its completed recruit without losing the job; freeing a seat lets that recruit enter. A rally point returns recruitment to the field, and disembarking troops prefer the rotated front doorway.

“Barracks heal occupants and can deploy new recruits directly into their sixteen-seat garrison.”