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.

InputHandler.h

@@ -1,9 +1,7 @@
 /*
  * InputHandler.h - input abstraction and mapping to commands
  */
-#ifndef KTE_INPUT_HANDLER_H
-#define KTE_INPUT_HANDLER_H
-
+#pragma once
 #include <string>
 
 #include "Command.h"
@@ -24,6 +22,4 @@ public:
 	// Poll for input and translate it to a command. Non-blocking.
 	// Returns true if a command is available in 'out'. Returns false if no input.
 	virtual bool Poll(MappedInput &out) = 0;
-};
-
-#endif // KTE_INPUT_HANDLER_H
+};