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/@babel/helper-create-class-features-plugin/README.md

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+# @babel/helper-create-class-features-plugin
+
+> Compile class public and private fields, private methods and decorators to ES6
+
+See our website [@babel/helper-create-class-features-plugin](https://babeljs.io/docs/babel-helper-create-class-features-plugin) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save @babel/helper-create-class-features-plugin
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/helper-create-class-features-plugin
+```