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/core-js/internals/get-built-in-node-module.js

@@ -0,0 +1,15 @@
+'use strict';
+var globalThis = require('../internals/global-this');
+var IS_NODE = require('../internals/environment-is-node');
+
+module.exports = function (name) {
+  if (IS_NODE) {
+    try {
+      return globalThis.process.getBuiltinModule(name);
+    } catch (error) { /* empty */ }
+    try {
+      // eslint-disable-next-line no-new-func -- safe
+      return Function('return require("' + name + '")')();
+    } catch (error) { /* empty */ }
+  }
+};