MPU-9250 provides magnetometer (auto north alignment), accelerometer
(elevation verification), and gyroscope (slew quality). BMP388 provides
pressure and temperature for atmospheric refraction correction at low
elevation angles. Both share I2C bus on GPIO8/9.
NimBLE-based Nordic UART Service (NUS) bridge on ESP32-S3-DevKitC-1.
Transparent passthrough: BLE client writes → UART1 TX → RS-422 → G2,
and G2 → RS-422 → UART1 RX → BLE notifications. USB serial serves as
debug monitor and fallback input.
Uses two MAX485 modules (one locked TX, one locked RX) with a SparkFun
BSS138 level converter for 3.3V/5V translation. Wiring schematic and
RJ-12 pinout documented in docs/ble-bridge-wiring.md.
