Add meter-reference calibration with saved ADC corrections, checked persistence and rollback. Preserve existing board coefficients and nRF52 voltage policy, and merge the Mini Repeater feature gates.
Validation: 69 focused tests, hosted documentation checks, and four firmware builds passed. Mini Repeater retains calibration and its existing filesystem with 376 flash bytes free; earlier Mini Sensor size failures remain documented.
mikecarper
ab6412e73c