Move UART command handlers into main/cmd/ for clearer layout.

Add cmd/ to CMake include paths and update documentation paths.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/ota_uart.h

@@ -17,7 +17,7 @@ typedef enum {
   OTA_UART_ST_BLOCK_ACK = 3,
   OTA_UART_ST_SUCCESS = 4,
   OTA_UART_ST_FAILED = 5,
-  /** ESP-NOW slave distribution in progress (see OTA_DIST_* in cmd_ota.c). */
+  /** ESP-NOW slave distribution in progress (see OTA_DIST_* in cmd/cmd_ota.c). */
   OTA_UART_ST_DISTRIBUTING = 6,
 } ota_uart_status_t;