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-jest/README.md

@@ -0,0 +1,25 @@
+# babel-jest
+
+[Babel](https://github.com/babel/babel) [jest](https://github.com/facebook/jest) plugin
+
+## Usage
+
+If you are already using `jest-cli`, add `babel-jest` and it will automatically compile JavaScript code using Babel.
+
+```bash
+yarn add --dev babel-jest @babel/core
+```
+
+If you would like to write your own preprocessor, uninstall and delete babel-jest and set the [config.transform](https://jestjs.io/docs/configuration#transform-object-string-string) option to your preprocessor.
+
+## Setup
+
+_Note: this step is only required if you are using `babel-jest` with additional code preprocessors._
+
+To explicitly define `babel-jest` as a transformer for your JavaScript code, map _.js_ files to the `babel-jest` module. Typescript files are also supported.
+
+```json
+"transform": {
+  "\\.[jt]sx?$": "babel-jest"
+},
+```