Introduce three new entities:
- Rocket Trooper: anti-armor infantry with shoulder-mounted guided rocket
- Constructor: unarmed tracked builder to replace lost commander build capacity
- Advanced Vehicle Plant: 4×4 factory with doubled production bays
Update AI composition weights and counter logic for the new units. Fix
byDef map to use Object.create(null) so the "constructor" key doesn't
shadow Object.prototype.constructor and silently poison gap calculations.
Add procedural art shapes for all three, register proc shapes in TARules,
update sprite frame assignments, and add core-structures assets.
