Idle builder units now automatically repair damaged allied structures
and units within their build range. A priority system ensures defensive
buildings are repaired before factories and other buildings. Auto-heal
orders are marked as non-player-assigned so explicit player orders
always take precedence. Builders can re-prioritize targets on a
retargeting cadence, similar to combat target acquisition.
Includes visual asset updates for TA arm and core units/structures.
Adjusts test to isolate passive self-heal from the new auto-heal mechanic.
