feat(bbb): add Morgan fingerprint extraction with shape/dtype guarantees

refactor(bbb): tighten is_valid_smiles signature; document RDLogger global effect

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

fix(core): apply level + propagate every call; tolerate pre-attached handlers

feat(core): add shared structured logger with idempotent handler attach

chore: bootstrap NeuroBridge project skeleton