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.

main.cc

@@ -1,15 +1,15 @@
+#include <cctype>
+#include <cstdio>
+#include <getopt.h>
 #include <iostream>
 #include <memory>
-#include <string>
-#include <cctype>
-#include <unistd.h>
-#include <getopt.h>
 #include <signal.h>
-#include <cstdio>
+#include <string>
+#include <unistd.h>
 #include <sys/stat.h>
 
-#include "Editor.h"
 #include "Command.h"
+#include "Editor.h"
 #include "Frontend.h"
 #include "TerminalFrontend.h"
 
@@ -22,6 +22,7 @@
 #  define KTE_VERSION_STR "devel"
 #endif
 
+
 static void
 PrintUsage(const char *prog)
 {