Add Arduino Uno rotator firmware

[Anton778]

Adds the Arduino Uno firmware for the OpenMCC two-axis AZ/EL rotator.

Included:

• compile-ready .ino for Arduino Uno + CNC Shield V3 + 2 x NEMA17;
• protocol compatible with the existing js/rotator.js panel (SET, STOP, HOME, PARK, STATUS);
• X axis used for AZ and Y axis for EL;
• X-/Y- end stops used for homing;
• non-blocking dual-axis stepping without external Arduino libraries;
• safety ranges AZ 0..360°, EL 0..90° and homing timeout;
• documentation with wiring and mandatory calibration notes;
• GitHub Actions compile check with Arduino CLI.

The mechanical transmission ratios remain deliberately set to 1.0 until the real SatNOGS v3 rotator is assembled and measured; hardware calibration is still required before accurate pointing.