Allow remote NAS deployment target

Prompts used since the previous commit:
- Ik wil dit testen op mijn NAS, die lokaal hier in huis draait. Dus niet op vps.australius.nl. Kan dat ook?

Special observations:
- deploy_vps.sh now accepts REMOTE_HOST and REMOTE_USER, with VPS_HOST/VPS_USER kept as aliases.
- The current service install path still assumes a Linux/systemd target with sudo; Synology/QNAP-style NAS deployment may need scheduler or container adaptation.
- verplaats_log.json remains modified from the user's run and was intentionally not staged.

deploy_vps.sh

@@ -1,8 +1,16 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-VPS_HOST="${VPS_HOST:-vps.austalius.nl}"
-VPS_USER="${VPS_USER:?Set VPS_USER to the non-root sudo SSH user}"
+REMOTE_HOST="${REMOTE_HOST:-${VPS_HOST:-}}"
+REMOTE_USER="${REMOTE_USER:-${VPS_USER:-}}"
+if [ -z "$REMOTE_HOST" ]; then
+  echo "Set REMOTE_HOST to the SSH host or IP address, for example a local NAS hostname." >&2
+  exit 2
+fi
+if [ -z "$REMOTE_USER" ]; then
+  echo "Set REMOTE_USER to the non-root sudo SSH user." >&2
+  exit 2
+fi
 APP_USER="${APP_USER:-mailcat}"
 APP_DIR="${APP_DIR:-/opt/mailcat}"
 SERVICE_NAME="${SERVICE_NAME:-mailcat-sort-backup}"
@@ -30,9 +38,9 @@ tar \
   -C "$ROOT_DIR" \
   -czf "$ARCHIVE" .
 
-scp "$ARCHIVE" "$VPS_USER@$VPS_HOST:/tmp/mailcat-deploy.tar.gz"
+scp "$ARCHIVE" "$REMOTE_USER@$REMOTE_HOST:/tmp/mailcat-deploy.tar.gz"
 
-ssh "$VPS_USER@$VPS_HOST" \
+ssh "$REMOTE_USER@$REMOTE_HOST" \
   "APP_USER='$APP_USER' APP_DIR='$APP_DIR' SERVICE_NAME='$SERVICE_NAME' ACCOUNT='$ACCOUNT' bash -s" <<'REMOTE'
 set -euo pipefail
 
@@ -46,7 +54,7 @@ sudo chown -R "$APP_USER:$APP_USER" "$APP_DIR" /var/lib/mailcat /var/log/mailcat
 sudo chmod 750 "$APP_DIR"
 
 if [ ! -f "$APP_DIR/config.json" ]; then
-  echo "Missing $APP_DIR/config.json on VPS. Create it with mode 600 before starting the service." >&2
+  echo "Missing $APP_DIR/config.json on remote host. Create it with mode 600 before starting the service." >&2
 fi
 sudo chmod 600 "$APP_DIR/config.json" 2>/dev/null || true
 sudo chown "$APP_USER:$APP_USER" "$APP_DIR/config.json" 2>/dev/null || true