Add sanoid Ansible role for ZFS snapshots and replication

Replaces manually deployed config files with a fully idempotent role:
installs sanoid, templates sanoid.conf and syncoid service/timer from
variables, enables both systemd timers. Removes static proxmox/sanoid.*
files. README rebuild section updated accordingly.

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

ansible/roles/sanoid/templates/syncoid.timer.j2

@@ -0,0 +1,11 @@
+[Unit]
+Description=Daily ZFS replication to HDD
+After=sanoid.timer
+
+[Timer]
+OnCalendar={{ syncoid_schedule }}
+RandomizedDelaySec={{ syncoid_randomized_delay }}
+Persistent=true
+
+[Install]
+WantedBy=timers.target