[codex] Add advisory CI design partner pilot runbook

[pengfei-threemoonslab]

Summary

• Add a design partner advisory CI pilot runbook with success criteria, partner fit, a paste-ready agent prompt, tracker fields, and outreach copy.
• Link the pilot from the design partner docs, docs index, and README.
• Update the Codex and target-repo guidance so the recommended agent install path includes advisory CI and agent instructions together.
• Clarify that agents-shipgate bootstrap alone does not satisfy the pilot because it does not install agent-instruction surfaces.

Validation

• Docs-only update; no Python code paths exercised.
• git diff --check origin/main...HEAD passed.