Code quality, safety, stability, and cleanups.

- Replace header include guards with `#pragma once` and perform minor optimizations.
- Replaced traditional include guards with `#pragma once` for simplicity and to reduce boilerplate in all headers.
- Improved CLI line number handling with clamping and error messaging.
- Enhanced `chdir` error handling for macOS GUI builds.
- Removed redundant logic for GUI builds.
- Adjusted font constructor and registry to handle `const` data pointers consistently.

KKeymap.h

@@ -1,9 +1,7 @@
 /*
  * KKeymap.h - mapping for k-command (C-k prefix) keys to CommandId
  */
-#ifndef KTE_KKEYMAP_H
-#define KTE_KKEYMAP_H
-
+#pragma once
 #include "Command.h"
 
 
@@ -29,6 +27,4 @@ KLowerAscii(const int key)
 	if (key >= 'A' && key <= 'Z')
 		return key + ('a' - 'A');
 	return key;
-}
-
-#endif // KTE_KKEYMAP_H
+}