v0.4.1: GHS precautionary text decode, interaction value units

GHS precautionary text decode, interaction value units

Precautionary (P-code) statements decode to standard GHS text; target interaction values carry the asserted uM unit.

Changed:

• pubchem_get_compound_safety precautionary statements decode to standard UN GHS Rev. 10 Annex 3 text via a new PRECAUTIONARY_STATEMENTS table (mirrors the existing PICTOGRAM_LABELS pattern); previously always "". #31
• pubchem_get_compound_interactions target-kind activity values carry the asserted uM unit (e.g. Ki = 0.0005 uM), grounded in PubChem's documented micromolar deposit convention; previously unitless. #32

337 tests pass; bun run devcheck clean.