feat(rag): ingest CLI (markdown/PDF → chunks → FAISS) + sample KB fixtures

feat(models): BBB classifier with predict_with_proba uncertainty

docs(mri): add build() docstring; fail-fast on unknown site label

test(mri): add deterministic synthetic NIfTI fixture (6 subjects × 2 sites)

docs(eeg): note MNE-pin coupling for fixture determinism

test(eeg): add deterministic synthetic Raw fixture (5 ch, 256 Hz, 10 s)

feat(bbb): add SMILES validity guard with RDKit + test fixture