Implements Godot 4.3+ visual particle VFX with GPUParticles2D/3D and ParticleProcessMaterial (emission, trails, subemitters, attractors, collision). Use when adding fire, smoke, rain, explosions, or polish bursts that are visual flavor, not gameplay state. Not for reading GPU particle positions for hit/loot logic, Three.js particles, or Compatibility-renderer trails/attractors.
