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/sanoid.conf

@@ -0,0 +1,28 @@
+# VM disks on SSD pool — snapshot daily/weekly
+[rpool/data]
+    use_template = vms
+    recursive = yes
+
+# Proxmox OS root — lighter schedule, mainly for recovery
+[rpool/ROOT]
+    use_template = system
+    recursive = yes
+
+#############################
+[template_vms]
+    daily = 7
+    weekly = 4
+    monthly = 0
+    hourly = 0
+    frequently = 0
+    autosnap = yes
+    autoprune = yes
+
+[template_system]
+    daily = 3
+    weekly = 2
+    monthly = 0
+    hourly = 0
+    frequently = 0
+    autosnap = yes
+    autoprune = yes

proxmox/syncoid.service

@@ -0,0 +1,8 @@
+[Unit]
+Description=Syncoid ZFS replication to HDD
+After=zfs.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/sbin/syncoid --recursive --no-privilege-elevation rpool/data hdd/backups/rpool-data
+ExecStart=/usr/sbin/syncoid --no-privilege-elevation rpool/ROOT/pve-1 hdd/backups/pve-root

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