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/lodash/defaultTo.js

@@ -0,0 +1,25 @@
+/**
+ * Checks `value` to determine whether a default value should be returned in
+ * its place. The `defaultValue` is returned if `value` is `NaN`, `null`,
+ * or `undefined`.
+ *
+ * @static
+ * @memberOf _
+ * @since 4.14.0
+ * @category Util
+ * @param {*} value The value to check.
+ * @param {*} defaultValue The default value.
+ * @returns {*} Returns the resolved value.
+ * @example
+ *
+ * _.defaultTo(1, 10);
+ * // => 1
+ *
+ * _.defaultTo(undefined, 10);
+ * // => 10
+ */
+function defaultTo(value, defaultValue) {
+  return (value == null || value !== value) ? defaultValue : value;
+}
+
+module.exports = defaultTo;