Add sanoid/syncoid ZFS snapshot and replication config

- sanoid: daily snapshots (7d) + weekly (4w) for rpool/data (VM disks)
  and rpool/ROOT (Proxmox OS); runs every 15 min via systemd timer
- syncoid: daily replication from rpool/data and pve-root to hdd/backups
  at 02:00; first full sync completed successfully
- All VM disks (gitea, monitoring) now backed up to HDD pool

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

proxmox/syncoid.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Daily ZFS replication to HDD
+After=sanoid.timer
+
+[Timer]
+OnCalendar=*-*-* 02:00:00
+RandomizedDelaySec=10min
+Persistent=true
+
+[Install]
+WantedBy=timers.target