Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/eslint/lib/cli-engine/xml-escape.js

@@ -0,0 +1,34 @@
+/**
+ * @fileoverview XML character escaper
+ * @author George Chung
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Public Interface
+//------------------------------------------------------------------------------
+
+/**
+ * Returns the escaped value for a character
+ * @param {string} s string to examine
+ * @returns {string} severity level
+ * @private
+ */
+module.exports = function(s) {
+    return (`${s}`).replace(/[<>&"'\x00-\x1F\x7F\u0080-\uFFFF]/gu, c => { // eslint-disable-line no-control-regex -- Converting controls to entities
+        switch (c) {
+            case "<":
+                return "&lt;";
+            case ">":
+                return "&gt;";
+            case "&":
+                return "&amp;";
+            case "\"":
+                return "&quot;";
+            case "'":
+                return "&apos;";
+            default:
+                return `&#${c.charCodeAt(0)};`;
+        }
+    });
+};