Refine help text, keybindings, GUI themes, and undo system.

- Expanded help text and command documentation with detailed keybinding descriptions.
- Added theme customization support to GUIConfig (Nord default, light/dark variants).
- Adjusted for consistent indentation and debug instrumentation in undo system.
- Enhanced test cases for multi-line, UTF-8, and branching scenarios.

HelpText.h

@@ -8,10 +8,10 @@
 
 class HelpText {
 public:
-    // Returns the embedded help text as a single string with newlines.
-    // Project maintainers can customize the returned string below
-    // (in HelpText.cc) without touching the help command logic.
-    static std::string Text();
+	// Returns the embedded help text as a single string with newlines.
+	// Project maintainers can customize the returned string below
+	// (in HelpText.cc) without touching the help command logic.
+	static std::string Text();
 };
 
 #endif // KTE_HELPTEXT_H