Standardise the sensor section with a `unit` column carrying the raw-value
unit (mBar, 0,1°C, mA, mV, %), placed in the same sub-header column as the
Parameters' unit. Bitfield registers (LevelSensors) correctly stay without a
unit. Document the per-category sheet column convention in the README so the
layout is enforced going forward.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>