- Initialize PI4IOE5V6408 I2C GPIO expander for RF switch/LNA control
- Fix I2C bus pins (SDA=10, SCL=8) - ESP32-C6 only has one I2C peripheral
- Remove SX126X_RXEN=5 (RF switch is on expander, not ESP32 GPIO)
- Set flash size to 16MB (actual hardware, was defaulting to 4MB)
- Remove P_LORA_TX_LED=15 (GPIO15 is OLED reset, not TX LED)
- Fix TCXO voltage 1.8V -> 3.0V
- Remove unused GPS_RX/GPS_TX defines
- Add esp_mac.h include for ESP32-C6 BLE builds
- Add WiFi companion radio build target