update backup/DR docs and runbooks for 3-2-1 architecture
- Full rewrite of backup-dr.md: 3-2-1 strategy with sda backup disk,
PVC file-level copy from LVM snapshots, pfsense backup, two offsite
paths. 4 Mermaid diagrams (data flow, timeline, disk layout, restore tree).
- Update storage.md: 65 proxmox-lvm PVCs, sda backup tier
- Update restore-full-cluster.md: add Phase 3.5 for PVC restore from sda
- Update restore-{mysql,postgresql,vault,vaultwarden}.md: add sda fallback paths
- New runbook: restore-pvc-from-backup.md (file-level restore from sda)
- Update CLAUDE.md Storage & Backup section for 3-2-1 architecture
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