Contacts.Step exchanges normal velocity between touching hull discs (PostCollisionVelocity moved verbatim
from ShieldManager) and publishes Zone.Contacted; ShieldManager presents it; HullCollider.OnCollisionEnter
and ShieldManager's ship-on-ship branch are deleted. Not yet built or tested (verification follows).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>