docs: upgrade, rollback, and operational procedures for enterprise deployment

[shaneutt]

Summary

Write operational documentation covering upgrade, rollback, and day-2 procedures for enterprise Praxis deployments.

Scope

• Upgrade procedures: version-to-version upgrade steps, config migration notes, pre-upgrade checklist
• Rollback procedures: how to revert to a previous version, config compatibility constraints, data migration rollback (response store schema)
• Dynamic reload: what can and cannot be hot-reloaded (filter pipelines yes; listener topology, protocol type, TLS toggle no)
• Health checks and readiness: verifying a deployment is healthy post-upgrade
• Troubleshooting: common failure modes, diagnostic commands, log interpretation
• Operational runbook: backup, restore, certificate rotation, credential rotation