Why:
- Experiment list and detail responses showed raw IDs instead of filenames
- No way to delete experiments from the UI
Changes:
- Add document_filename field to ExperimentDetailResponse
- Enrich list endpoint with filenames and calculated best_strategy from aggregate_metrics
- Add DELETE /experiments/{id} endpoint
Impact:
- API responses now include document_filename for all experiment endpoints
- Frontend can display filenames instead of IDs