Convert a value between units of measure: mass (g, kg, mg, lb, oz, t, st), length (m, km, cm, mm, in, ft, yd, mi), volume (l, ml, m3, gal, gal-imp, qt, pt, cup, floz, tbsp, tsp), area (m2, km2, ft2, acre, ha), and temperature (C, F, K). Units are matched case-insensitively with common aliases (kg/kilogram/kgs). Returns {value, from, to, dimension, result}. Exact factors — the ground-truth answer a CPG/ETL pipeline needs instead of an LLM approximating conversions. Cross-dimension conversions (kg→m) return 400.