Docs: add enterprise agent deployment-readiness guidance for contributors

Proposal\nAdd a short section in CONTRIBUTING.md for production-oriented docs contributions (agent deployment readiness).\n\n### Suggested checklist themes\n- secrets and credential boundaries\n- tool execution controls / approval boundaries\n- tracing and observability expectations\n- rollback strategy for prompt/config changes\n\n## Why this helps\nSemantic Kernel is used in enterprise environments where deployment reliability and auditability matter. A concise contribution shape can improve docs quality and review speed.\n\nIf this aligns with maintainers' direction, I can send a docs PR draft.

Start by reading CONTRIBUTING.md and identify the appropriate place for contributor guidance. Add a concise production-oriented checklist covering secrets and credential boundaries, tool execution and approval controls, tracing and observability, and rollback for prompt or configuration changes; it is done when these themes are clearly documented in that file.