chore: register Atrinik service updater

[zoeyrose]

Summary

Register the new public atrinik/service-updater repository (ID 1403857103) in Atrinik's desired-state inventory so its PR policy, release tags and repository properties can be governed.

Implementation / behavior

• Add the main-branch PR gate with Updater validation and Conventional PR title contexts, plus semantic-release tag protection.
• Classify the MIT updater as active shared infrastructure/service code with semantic-release ownership.
• Preserve all existing repository entries, organization controls and package grants.

Validation

• Independent policy review found no structural defects.
• JSON validation, repository validator, Bash syntax, all 17 policy tests and whitespace checks passed.
• Both publishers produced reviewed plan-only output. The audit currently reports only the five expected new-repository drifts.
• Required ShellCheck was run in the cached pinned Linux tool image; no workflows are changed here.

Limitations / follow-up

No policy has been applied. Apply must wait until the new updater's reviewed bootstrap source lands on main and Updater validation passes. Public container availability is verified by the owning implementation separately.