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.

HighlighterRegistry.h

@@ -0,0 +1,26 @@
+// HighlighterRegistry.h - create/detect language highlighters
+#pragma once
+
+#include <functional>
+#include <memory>
+#include <string>
+#include <string_view>
+
+#include "LanguageHighlighter.h"
+
+namespace kte {
+
+class HighlighterRegistry {
+public:
+    // Create a highlighter for normalized filetype id (e.g., "cpp", "json", "markdown", "shell", "go", "python", "rust", "lisp").
+    static std::unique_ptr<LanguageHighlighter> CreateFor(std::string_view filetype);
+
+    // Detect filetype by path extension and shebang (first line).
+    // Returns normalized id or empty string if unknown.
+    static std::string DetectForPath(std::string_view path, std::string_view first_line);
+
+    // Normalize various aliases/extensions to canonical ids.
+    static std::string Normalize(std::string_view ft);
+};
+
+} // namespace kte