feat: add oneshot systemd service for scheduled backup check

deploy/ns8-backup-monitor-check.service

@@ -0,0 +1,25 @@
+# ns8-backup-monitor-check.service
+#
+# One-shot systemd service that runs the scheduled backup recap check.
+# Invoked by ns8-backup-monitor-check.timer — not managed directly.
+#
+# This service reads backup status from the NS8 cluster Redis, classifies
+# the outcome (SUCCESS / PARTIAL / REPO_FAILURE), and sends a recap email
+# via ns8-sendmail. It is the scheduled counterpart to the Alertmanager
+# webhook path, which only fires on failures.
+[Unit]
+Description=ns8-backup-monitor scheduled backup status check
+After=network.target ns8-backup-monitor.service
+# Do not block startup if the main service is not running
+Wants=ns8-backup-monitor.service
+
+[Service]
+Type=oneshot
+# Run as root to access the NS8 Redis socket and ns8-sendmail
+User=root
+ExecStart=/usr/bin/python3 -m ns8_backup_monitor.scheduled_check
+WorkingDirectory=/opt/ns8-backup-monitor
+# Capture stdout and stderr to the journal
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=ns8-backup-monitor-check