docs(trivium): define bridge rule states

[Illian-Amerond]

Summary

• Adds bridge rule states to the Trivium Chat Codex Exchange Register.
• Separates private source updates, routine public projection updates, and first public entries/new publication surfaces.
• Records that first public entries are stricter than routine maintenance but do not become a publication event without a separate package.

Calibration Note

This PR is intentionally using the public branch protection path after the initial register landed by admin bypass. It should exercise Docs Link Check / links before merge.