docs: finalize ProChat closeout revision record

[stevewesthoek]

Summary

• Keep the milestone marked complete while distinguishing deployed runtime 59a9c61 from later source-main documentation commits.
• Record that post-deployment closeout edits are documentation-only and do not redeploy production.
• Keep the implementation plan's validation section marked complete.

Validation

• Documentation links are valid.
• ✅ Environment documentation is synchronized.
• Documentation-only; repository workflow skips production deployment.