Replace cron suggestion with systemd timer for kiwix updates

User units in systemd/ with an install.sh that symlinks and enables.
Persistent=true means missed runs (machine off) catch up on next boot.
Logs via journald: journalctl --user -u kiwix-update.service

https://claude.ai/code/session_012gDnantBmFTWZGCiKyjazx

systemd/kiwix-update.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Monthly Kiwix ZIM update check
+Requires=kiwix-update.service
+
+[Timer]
+OnCalendar=monthly
+RandomizedDelaySec=1h
+Persistent=true
+
+[Install]
+WantedBy=timers.target