Add syntax highlighting infrastructure

- Introduced `HighlighterRegistry` with support for multiple language highlighters (e.g., JSON, Markdown, Python).
- Added `JsonHighlighter` implementation for basic JSON syntax highlighting.

GUIConfig.h

@@ -12,14 +12,18 @@
 
 class GUIConfig {
 public:
-	bool fullscreen   = false;
-	int columns       = 80;
-	int rows          = 42;
-	float font_size   = (float) KTE_FONT_SIZE;
-	std::string theme = "nord";
-	// Background mode for themes that support light/dark variants
-	// Values: "dark" (default), "light"
-	std::string background = "dark";
+    bool fullscreen   = false;
+    int columns       = 80;
+    int rows          = 42;
+    float font_size   = (float) KTE_FONT_SIZE;
+    std::string theme = "nord";
+    // Background mode for themes that support light/dark variants
+    // Values: "dark" (default), "light"
+    std::string background = "dark";
+
+    // Default syntax highlighting state for GUI (kge): on/off
+    // Accepts: on/off/true/false/yes/no/1/0 in the ini file.
+    bool syntax = true; // default: enabled
 
 	// Load from default path: $HOME/.config/kte/kge.ini
 	static GUIConfig Load();