enrich: add concurrency_limit=1 to prevent DuckDB stale lock from overlapping runs
If a run gets stuck and a new one starts, both pods share the same
/prefect-analytics/analytics.duckdb hostPath and conflict. concurrency_limit=1
ensures only one run is active at a time.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>