- Add SwitchImuSample struct and IMU fields to SwitchInputState
- Add fill_imu_report_data() to pack samples into imuData[36]
- Rewrite switch_pro_apply_uart_packet() for v2 with checksum validation
- Enlarge poll_uart_frames() buffer to 64 bytes for variable-length frames
- Clear imu_sample_count after each USB report send (prevent stale IMU)