Introduce file picker and GUI configuration with enhancements.

- Add visual file picker for GUI with toggle support.
- Introduce `GUIConfig` class for loading GUI settings from configuration file.
- Refactor window initialization to support dynamic sizing based on configuration.
- Add macOS-specific handling for fullscreen behavior.
- Improve header inclusion order and minor code cleanup.

GUIInputHandler.h

@@ -4,11 +4,12 @@
 #ifndef KTE_GUI_INPUT_HANDLER_H
 #define KTE_GUI_INPUT_HANDLER_H
 
-#include <queue>
 #include <mutex>
+#include <queue>
 
 #include "InputHandler.h"
 
+
 union SDL_Event; // fwd decl to avoid including SDL here (SDL defines SDL_Event as a union)
 
 class GUIInputHandler final : public InputHandler {