Proven end-to-end

A milestone rather than a feature. A scripted end-to-end demo now boots the registry, signs in, creates an org and a registry, publishes several skills, installs them into a fresh project, publishes one more, and watches skillhub sync pick it up — with git status clean the entire time. Every core safety, authorization, and deterministic-packaging guarantee is audited with evidence, proving the pieces actually hold together.