[codex] Tighten adoption prompt guidance

[joerucci]

Summary

Tightens Ghostable's generated adoption prompt so coding agents make evidence-backed recommendations and avoid overstating what can be inferred from environment keys alone.

Changes

• Require annotation recommendations to be supported by Ghostable metadata, repo files, deployment config, CI config, framework config, or user-provided context.
• Tell agents not to invent owner/team, provider, deploy-managed status, agent visibility, or rotation policy, and to move unknown fields into open questions.
• Clarify that hygiene report --unused findings are heuristic and that stored-but-unreferenced keys are not necessarily safe to delete.
• Add guidance for non-git ghostable review --env-only --json failures so agents continue with other read-only checks.
• Update adoption prompt and setup wizard copy tests.

Validation

• make check