chore: Guard ESC debug output behind compile flag (Issue #521)

- esc_hoverboard.c: huart2 static in production; non-static only under
  #ifdef DEBUG_MOTOR_TEST (needed by R command in jetson_uart.c)
- esc_hoverboard.c: UART5 diagnostic in hoverboard_backend_init() and
  per-packet printf in hoverboard_backend_send() guarded by same flag
- esc_hoverboard.c: #include <stdio.h> also guarded (not needed in production)
- jetson_uart.c: R (baud sweep) and X (GPIO test) commands guarded by
  #ifdef DEBUG_MOTOR_TEST — not compiled into production firmware

Production build: no debug output, static huart2, no R/X commands.
Debug build: define DEBUG_MOTOR_TEST to re-enable all diagnostics.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/esc_hoverboard.c

@@ -1,7 +1,9 @@
 #include "esc_backend.h"
 #include "config.h"
 #include "stm32f7xx_hal.h"
+#ifdef DEBUG_MOTOR_TEST
 #include <stdio.h>
+#endif
 
 /*
  * Hoverboard ESC Backend Implementation
@@ -25,7 +27,11 @@ typedef struct __attribute__((packed)) {
     uint16_t checksum;
 } hoverboard_cmd_t;
 
-UART_HandleTypeDef huart2;  /* non-static: accessed by jetson_uart.c raw test */
+#ifdef DEBUG_MOTOR_TEST
+UART_HandleTypeDef huart2;  /* non-static: exposed for jetson_uart.c R command */
+#else
+static UART_HandleTypeDef huart2;
+#endif
 
 /* Backend vtable instance */
 static const esc_backend_t hoverboard_backend;
@@ -66,6 +72,7 @@ static void hoverboard_backend_init(void) {
     huart2.Init.OverSampling = UART_OVERSAMPLING_16;
     HAL_UART_Init(&huart2);
 
+#ifdef DEBUG_MOTOR_TEST
     /* Diagnostic: report UART5 register state on USART6 after init */
     {
         extern void jetson_uart_send(const uint8_t *data, uint16_t len);
@@ -87,13 +94,16 @@ static void hoverboard_backend_init(void) {
         HAL_Delay(100);
         jetson_uart_send((uint8_t*)diag, n);
     }
+#endif /* DEBUG_MOTOR_TEST */
 }
 
 /*
  * Send motor command via hoverboard protocol.
  * Called at ~50Hz from motor_driver_update().
  */
+#ifdef DEBUG_MOTOR_TEST
 static volatile uint32_t hover_tx_count = 0;
+#endif
 
 static void hoverboard_backend_send(int16_t speed, int16_t steer) {
     hoverboard_cmd_t cmd;
@@ -102,6 +112,7 @@ static void hoverboard_backend_send(int16_t speed, int16_t steer) {
     cmd.speed = speed;
     cmd.checksum = cmd.start ^ cmd.steer ^ cmd.speed;
 
+#ifdef DEBUG_MOTOR_TEST
     HAL_StatusTypeDef rc = HAL_UART_Transmit(&huart2, (uint8_t *)&cmd, sizeof(cmd), 5);
     hover_tx_count++;
 
@@ -113,6 +124,9 @@ static void hoverboard_backend_send(int16_t speed, int16_t steer) {
             (unsigned long)hover_tx_count, (int)rc, speed, steer);
         jetson_uart_send((uint8_t*)dbg, n);
     }
+#else
+    HAL_UART_Transmit(&huart2, (uint8_t *)&cmd, sizeof(cmd), 5);
+#endif
 }
 
 /*

src/jetson_uart.c

@@ -177,6 +177,7 @@ static void process_line(const char *buf, uint8_t len) {
             break;
         }
 
+#ifdef DEBUG_MOTOR_TEST
         /* GPIO test: reconfigure PC12 as plain GPIO output, set HIGH for 10s, then restore UART */
         case 'X': {
             GPIO_InitTypeDef gpio = {0};
@@ -252,6 +253,7 @@ static void process_line(const char *buf, uint8_t len) {
             HAL_UART_Transmit(&huart6, (uint8_t*)ack, 7, 10);
             break;
         }
+#endif /* DEBUG_MOTOR_TEST */
 
         case '?': {
             /* Status dump for debugging */