Replace global Polars dataframes in src/utils.py (lines 891-913) with
an on-disk DuckDB database, built at startup from decp_prod.parquet.
Keeps two small search-path frames (df_acheteurs, df_titulaires) in
memory; moves heavy filtering and aggregation to DuckDB via a
query_marches helper that returns pl.DataFrame.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Colin Maudry