docs(systemd): fix paths + add dashboard smoke + vendor units

scripts/smoke_dashboard.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+HOST="${SECOND_BRAIN_HOST:-127.0.0.1}"
+PORT="${SECOND_BRAIN_PORT:-${PORT:-8501}}"
+BASE_URL="http://${HOST}:${PORT}"
+
+if command -v systemctl >/dev/null 2>&1; then
+  if ! systemctl is-active --quiet openclaw-secondbrain-dashboard.service; then
+    echo "ERROR: openclaw-secondbrain-dashboard.service is not active" >&2
+    exit 1
+  fi
+fi
+
+curl -fsS "${BASE_URL}/healthz" >/dev/null
+
+stats_json="$(curl -fsS "${BASE_URL}/api/stats")"
+python3 -c 'import json,sys; json.load(sys.stdin)' <<<"$stats_json"
+
+echo "OK: dashboard smoke test passed (${BASE_URL})"