Add new response types and parameters for logs API:
- Add GroupedStatsItem and GroupedStatsResponse definitions
- Add ListLogsResponse and LogView definitions for detailed log records
- Add group_by enum parameter (model/day/month) to stats endpoint
- Update endpoint descriptions to clarify response types and request_body inclusion
- Update response schema references to use correct types
Add group_by parameter to /admin/logs/stats endpoint supporting:
- group_by=model: aggregate stats per model with avg latency
- group_by=day: daily aggregation with token counts
- group_by=month: monthly aggregation with token counts
Also include request_body field in admin ListLogs response for
full visibility into logged requests.
