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/@pmmmwh/react-refresh-webpack-plugin/overlay/components/Spacer.js

@@ -0,0 +1,19 @@
+/**
+ * @typedef {Object} SpacerProps
+ * @property {string} space
+ */
+
+/**
+ * An empty element to add spacing manually.
+ * @param {Document} document
+ * @param {HTMLElement} root
+ * @param {SpacerProps} props
+ * @returns {void}
+ */
+function Spacer(document, root, props) {
+  const spacer = document.createElement('div');
+  spacer.style.paddingBottom = props.space;
+  root.appendChild(spacer);
+}
+
+module.exports = Spacer;