This commit introduces a new Modbus input register for the system's supply voltage.
- The `modbus-registers.de.md` documentation is updated to include the `SUPPLY_VOLTAGE_MV` register at address `0x00F5` within the system block.
- The `modbus_server.h` header defines the new register.
- The `modbus_server.c` implementation provides a fixed value (12300 mV) for this register.
- The `modbus_tool.py` script is updated to read and display this new supply voltage value in the UI.
This lays the groundwork for integrating actual voltage measurements in the future.
Eduard Iten