fix: support catalog-qualified benchmark databases

[zgxme]

Summary

• add Doris and StarRocks helpers to qualify benchmark databases with the configured catalog
• apply catalog-qualified database names to SQL execution, table listing, stats, plan, version and JDBC datasource paths
• qualify bare table names for row-count queries while preserving explicitly qualified names

Verification

• bash -n engines/doris_engine.sh
• bash -n engines/starrocks_engine.sh
• git diff --cached --check