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/@sinonjs/commons/lib/global.js

@@ -0,0 +1,22 @@
+"use strict";
+
+/**
+ * A reference to the global object
+ *
+ * @type {object} globalObject
+ */
+var globalObject;
+
+/* istanbul ignore else */
+if (typeof global !== "undefined") {
+    // Node
+    globalObject = global;
+} else if (typeof window !== "undefined") {
+    // Browser
+    globalObject = window;
+} else {
+    // WebWorker
+    globalObject = self;
+}
+
+module.exports = globalObject;