Fix warm-up blocking: use LIMIT 1 instead of COUNT(*)

COUNT(*) on large tables (CNPJ, RAIS) held the lock for 30s+ each,
blocking all incoming queries during startup. LIMIT 1 warms the S3
file-listing cache in < 1s per table without reading all Parquet footers.

auth.py

@@ -75,7 +75,7 @@ def _warm_cache():
     for t in hot_tables:
         try:
             with _lock:
-                _con.execute(f"SELECT COUNT(*) FROM basedosdados.{t}")
+                _con.execute(f"FROM basedosdados.{t} LIMIT 1")
         except Exception:
             pass