Use local board.h include in firmware main

Replace the relative include path to `board.h` in `gd32_dmx_usb_pro/firmware/main.cpp` with the project include form. This reduces path fragility and aligns with include path configuration.

Author: vanvught

gd32_dmx_usb_pro/firmware/main.cpp

@@ -31,7 +31,7 @@
 #include "widgetparams.h"
 #include "configstore.h"
 #include "software_version.h"
-#include "../../lib-board/include/board.h"
+#include "board.h"
 
 #ifndef ALIGNED
 #define ALIGNED __attribute__((aligned(4)))