v3.7: unify preference_pairs (combine within+cross); leak-free chain-level verified

v3.6: rescue all 72,510 swap_complexes rows via cluster co-occurrence components; exact 80/10/10 split, leak-free

v3.5: combine within+cross into unified swap_complexes & swap_relationships; reseed splits (cluster 75/12.5/12.5, seed 0089) for ~80/10/10 row split

v3.4: drop same-species rows and TimeTree no-data pairs; refresh splits

Make train/val/test proper HF splits: per-split parquets + YAML data_files

Make train/val/test proper HF splits: per-split parquets + YAML data_files