refactor(ecs): make systems own component signatures

[czlin7]

Summary

• make each system declare its required ECS component signature
• register the signature automatically inside SystemManager::RegisterSystem<T>()
• remove manual SetSignature<T>() calls and duplicated signature knowledge from SimulationWorld
• update foundation tests so registration alone establishes correct system membership

Why

A system's required component set is part of that system's definition. Keeping registration and signature assignment as separate external steps made it possible to register a system successfully but silently leave it unable to receive matching entities.

This refactor keeps that invariant local to each system and reduces SimulationWorld to deciding which systems exist.

Scope

• behavior-preserving ECS registration refactor
• no component-index redesign
• no new abstraction layer or runtime registration framework

Validation

• branch is 1 commit ahead of develop and 0 behind
• changed files are limited to the three systems, SystemManager, SimulationWorld, and foundation tests