Refactor syntax highlighting infrastructure and related classes.

- Moved all language highlighter implementations (`CppHighlighter`, `GoHighlighter`, `JsonHighlighter`, etc.), the engine, and registry to `syntax/`.

themes/ThemeHelpers.h

@@ -0,0 +1,17 @@
+#ifndef KTE_THEMEHELPERS_H
+#define KTE_THEMEHELPERS_H
+
+#include "imgui.h"
+
+// Small helper to convert packed RGB (0xRRGGBB) + optional alpha to ImVec4
+static ImVec4
+RGBA(const unsigned int rgb, float a = 1.0f)
+{
+	const float r = static_cast<float>(rgb >> 16 & 0xFF) / 255.0f;
+	const float g = static_cast<float>(rgb >> 8 & 0xFF) / 255.0f;
+	const float b = static_cast<float>(rgb & 0xFF) / 255.0f;
+	return {r, g, b, a};
+}
+
+
+#endif //KTE_THEMEHELPERS_H