Removes mlp/training/eval/backtest/metrics_detail/calibration and the old example trainers. Preserves multi_horizon_labels, purged_split, fxcache_reader (Phase A data path), mamba2_block (gate reference). Subsequent commits populate cfc/heads/isv/pinned/trainer/data/gate. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>