docs: create guide for moving to production

[frrist]

Summary

Create a guide for operators to migrate from staging (warm-staging) to production (forge-prod).

Context

From PR #427 review feedback - the operator guide mentions starting on warm-staging to verify setup, then moving to forge-prod, but there's no dedicated guide for this transition.

Suggested Content

• Pre-production checklist
• Configuration changes needed
• Data migration considerations (if any)
• Verification steps after switching
• Common pitfalls to avoid

References

• PR docs: write operator guide docs #427 comment: docs: write operator guide docs #427
• Related docs: docs/content/operator-guide/joining.md