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.service.j2

@@ -0,0 +1,9 @@
+[Unit]
+Description=Syncoid ZFS replication to HDD
+After=zfs.target
+
+[Service]
+Type=oneshot
+{% for job in syncoid_jobs %}
+ExecStart=/usr/sbin/syncoid --no-privilege-elevation{% if job.recursive %} --recursive{% endif %} {{ job.src }} {{ job.dst }}
+{% endfor %}