fix: explain duckdb failures caused by job isolation

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/ee-repo-ref.txt

@@ -1 +1 @@
-181fa0c206d7f84a289b4396a7f7764bc815d284
+9b6e7cac8d757283ef5455d16749810dfa4a9330

backend/windmill-worker/src/duckdb_executor.rs

@@ -1641,6 +1641,8 @@ pub async fn do_duckdb(
         let (result, column_order) = match result {
             Ok(r) => r,
             Err(e) => {
+                #[cfg(feature = "private")]
+                let e = crate::duckdb_isolation_ee::explain_error(e);
                 if let Some((_, meta)) = &materialize {
                     record_mat(
                         conn,