Add StatefulSets page with diagram - New StatefulSets.md (FR): stable identity (ordinal names, headless DNS, per-Pod storage), when to use, OrderedReady ordering, manifest (Service + StatefulSet volumeClaimTemplates), Deployment vs StatefulSet, kubectl cmds - New images/statefulset.svg (StatefulSet -> web-0/1/2 -> one PVC each) - Add page to Home and _Sidebar; update AGENTS.md page list