Litestream replication to the NAS and nightly media backup

Add a litestream service (0.5.17) to the compose stack that streams
/data/mealquest.db over SFTP to the Synology NAS with a dedicated key,
daily snapshots kept for a week. Add a systemd timer that rsyncs the
media directory to the NAS nightly at 03:30.

Task: d2f2e87e-5114-4ef1-93ab-360ffb5c009e

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

deploy/systemd/mealquest-media-backup.service

@@ -0,0 +1,13 @@
+# Runs the nightly MealQuest media backup (/usr/local/sbin/mealquest-media-backup).
+# Triggered by mealquest-media-backup.timer; run by hand with
+#   systemctl start mealquest-media-backup
+# and read the result with
+#   journalctl -u mealquest-media-backup
+[Unit]
+Description=Back up MealQuest media to the Synology NAS
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/sbin/mealquest-media-backup