feat(simulation): add metabolism and starvation

[czlin7]

Summary

• add a MetabolismSystem that consumes entity energy using simulation dt
• apply starvation damage after energy reaches zero
• destroy entities when starvation reduces health to zero
• register metabolism in SimulationWorld using the existing CEnergy + CHealth signature
• add regression coverage for energy consumption, starvation damage, and death cleanup

Why

CEnergy and CHealth already exist on spawned animals but previously had no simulation behaviour. This introduces the first life-state progression on top of the deterministic fixed-step foundation.

Design notes

• structural entity destruction is deferred until after iterating the system membership set to avoid mutating the collection during iteration
• metabolism runs before AI and movement so life state can later feed behaviour decisions

Validation

• branch is one commit ahead of develop
• changed scope is limited to the new metabolism system, SimulationWorld integration, and foundation tests