- Replace deprecated `date` parameter with `start_date`/`end_date`
- Return single-date format (detailed) when dates are equal
- Return range format (lightweight with period metrics) when dates differ
- Add period metrics: period_return_pct, annualized_return_pct, calendar_days, trading_days
- Default to last 30 days when no dates provided
- Group results by model for date range queries
- Add comprehensive test coverage for both response formats
- Implement automatic edge trimming for date ranges
- Add 404 error handling for empty result sets
- Include 422 error for deprecated `date` parameter usage
