fix(autotune): wrap pd.Timestamp in try/except so bad dates surface as ValueError

feat(autotune): apply_tuning helper for Forecast tab pre-fill

feat(autotune): run_autotune orchestrator with heatmap output

feat(autotune): backtest_core pure metrics

feat(autotune): save_tuning + load_tuning with replace-on-conflict

feat(autotune): tuning_results table init