- Fix 'name pd is not defined' error in _get_stock_stats_bulk by adding missing pandas import
- Add ensure_ascii=False to json.dump() to properly display Chinese characters in log files
Add _clean_dataframe() to normalize stock DataFrames before stockstats:
coerce invalid dates/prices, drop rows missing Close, fill price gaps.
Also add on_bad_lines="skip" to all cached CSV reads.